Integrated operation of molten carbonate fuel cells

ABSTRACT

In various aspects, systems and methods are provided for operating a molten carbonate fuel cell assembly at increased power density. This can be accomplished in part by performing an effective amount of an endothermic reaction within the fuel cell stack in an integrated manner. This can allow for increased power density while still maintaining a desired temperature differential within the fuel cell assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Ser. Nos. 61/787,587,61/787,697, 61/787,879, and 61/788,628, all filed on Mar. 15, 2013, eachof which is incorporated by reference herein in its entirety. Thisapplication also claims the benefit of U.S. Ser. Nos. 61/884,376,61/884,545, 61/884,565, 61/884,586, 61/884,605, and 61/884,635, allfiled on Sep. 30, 2013, each of which is incorporated by referenceherein in its entirety. This application further claims the benefit ofU.S. Ser. No. 61/889,757, filed on Oct. 11, 2013, which is incorporatedby reference herein in its entirety.

This application is related to 4 other co-pending, commonly assignedU.S. patent applications, filed on Mar. 5, 2014 as follows: Ser. No.14/197,391; 14/197,430; 14/197,551; and Ser. No. 14/197,613. Thisapplication is also related to the following 21 co-pending, commonlyassigned U.S. patent applications, filed on Mar. 13, 2014: Ser. Nos.14/207,686; 14/207,686; 14/207,688; 14/207,687; 14/207,690; 14/207,696;14/207,698; 14/207,704; 14/207,706; 14/207,691 14/207,693; 14/207,699;14/207,700; 14/207,705; 14/207,708; 14/207,711; 14/207,714; 14/207,710;14/207,712; 14/207,721; 14/207,726; 14/207,728. Each of these co-pendingU.S. applications is hereby incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

In various aspects, the invention is related to chemical productionand/or power generation processes integrated using molten carbonate fuelcells.

BACKGROUND OF THE INVENTION

Molten carbonate fuel cells utilize hydrogen and/or other fuels togenerate electricity. The hydrogen may be provided by reforming methaneor other reformable fuels in a steam reformer that is upstream of thefuel cell or within the fuel cell. Reformable fuels can encompasshydrocarbonaceous materials that can be reacted with steam and/or oxygenat elevated temperature and/or pressure to produce a gaseous productthat comprises hydrogen. Alternatively or additionally, fuel can bereformed in the anode cell in a molten carbonate fuel cell, which can beoperated to create conditions that are suitable for reforming fuels inthe anode. Alternately or additionally, the reforming can occur bothexternally and internally to the fuel cell.

Traditionally, molten carbonate fuel cells are operated to maximizeelectricity production per unit of fuel input, which may be referred toas the fuel cell's electrical efficiency. This maximization can be basedon the fuel cell alone or in conjunction with another power generationsystem. In order to achieve increased electrical production and tomanage the heat generation, fuel utilization within a fuel cell istypically maintained at 70% to 75%.

U.S. Published Patent Application 2011/0111315 describes a system andprocess for operating fuel cell systems with substantial hydrogencontent in the anode inlet stream. The technology in the '315publication is concerned with providing enough fuel in the anode inletso that sufficient fuel remains for the oxidation reaction as the fuelapproaches the anode exit. To ensure adequate fuel, the '315 publicationprovides fuel with a high concentration of H₂. The H₂ not utilized inthe oxidation reaction is recycled to the anode for use in the nextpass. On a single pass basis, the H₂ utilization may range from 10% to30%. The '315 reference does not describe significant reforming withinthe anode, instead relying primarily on external reforming.

U.S. Published Patent Application 2005/0123810 describes a system andmethod for co-production of hydrogen and electrical energy. Theco-production system comprises a fuel cell and a separation unit, whichis configured to receive the anode exhaust stream and separate hydrogen.A portion of the anode exhaust is also recycled to the anode inlet. Theoperating ranges given in the '810 publication appear to be based on asolid oxide fuel cell. Molten carbonate fuel cells are described as analternative.

U.S. Published Patent Application 2003/0008183 describes a system andmethod for co-production of hydrogen and electrical power. A fuel cellis mentioned as a general type of chemical converter for converting ahydrocarbon-type fuel to hydrogen. The fuel cell system also includes anexternal reformer and a high temperature fuel cell. An embodiment of thefuel cell system is described that has an electrical efficiency of about45% and a chemical production rate of about 25% resulting in a systemcoproduction efficiency of about 70%. The '183 publication does notappear to describe the electrical efficiency of the fuel cell inisolation from the system.

U.S. Pat. No. 5,084,362 describes a system for integrating a fuel cellwith a gasification system so that coal gas can be used as a fuel sourcefor the anode of the fuel cell. Hydrogen generated by the fuel cell isused as an input for a gasifier that is used to generate methane from acoal gas (or other coal) input. The methane from the gasifier is thenused as at least part of the input fuel to the fuel cell. Thus, at leasta portion of the hydrogen generated by the fuel cell is indirectlyrecycled to the fuel cell anode inlet in the form of the methanegenerated by the gasifier.

An article in the Journal of Fuel Cell Science and Technology (G.Manzolini et. al., J. Fuel Cell Sci. and Tech., Vol. 9, February 2012)describes a power generation system that combines a combustion powergenerator with molten carbonate fuel cells. Various arrangements of fuelcells and operating parameters are described. The combustion output fromthe combustion generator is used in part as the input for the cathode ofthe fuel cell. One goal of the simulations in the Manzolini article isto use the MCFC to separate CO₂ from the power generator's exhaust. Thesimulation described in the Manzolini article establishes a maximumoutlet temperature of 660° C. and notes that the inlet temperature mustbe sufficiently cooler to account for the temperature increase acrossthe fuel cell. The electrical efficiency (i.e. electricitygenerated/fuel input) for the MCFC fuel cell in a base model case is50%. The electrical efficiency in a test model case, which is optimizedfor CO₂ sequestration, is also 50%.

An article by Desideri et al. (Intl. J. of Hydrogen Energy, Vol. 37,2012) describes a method for modeling the performance of a powergeneration system using a fuel cell for CO₂ separation. Recirculation ofanode exhaust to the anode inlet and the cathode exhaust to the cathodeinlet are used to improve the performance of the fuel cell. The modelparameters describe an MCFC electrical efficiency of 50.3%.

U.S. Pat. No. 5,169,717 describes a method for integrating a moltencarbonate fuel cell with a system for production of ammonia. Theintegrated system uses a front end different from the molten carbonatefuel cell to process the input hydrogen and nitrogen streams forproduction of ammonia.

SUMMARY OF THE INVENTION

The operation of molten carbonate fuel cells can be integrated with avariety of processes for production of energy, production of hydrogen,syngas, or other fuels, and/or production of commercially usefulcompounds.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically shows an example of a configuration for moltencarbonate fuel cells and associated reforming and separation stages.

FIG. 2 schematically shows another example of a configuration for moltencarbonate fuel cells and associated reforming and separation stages.

FIG. 3 schematically shows an example of the operation of a moltencarbonate fuel cell.

FIG. 4 schematically shows an example of a combined cycle system forgenerating electricity based on combustion of a carbon-based fuel.

FIG. 5 schematically shows an example of a combined cycle system forgenerating electricity based on combustion of a carbon-based fuel.

FIGS. 6-8 schematically show examples of configurations for integratingmolten carbonate fuel cells with processes for generation ofhydrocarbonaceous compounds.

FIGS. 9 and 10 show results from simulations of integrated MCFC andFischer-Tropsch systems.

FIGS. 11 and 12 schematically show examples of configurations forintegrating molten carbonate fuel cells with processes for synthesis ofmethanol.

FIG. 13 shows process flow values from a calculation for an integratedMCFC and methanol synthesis process.

FIGS. 14-15 schematically show examples of configurations forintegrating molten carbonate fuel cells with fermentation processes.

FIG. 16 schematically shows an examples of a configuration forintegrating molten carbonate fuel cells with a process for synthesis ofa nitrogen-containing compound.

FIG. 17 schematically shows an example of integration of moltencarbonate fuel cells with a process for producing cement.

FIG. 18 shows process flows for an example of integration of moltencarbonate fuel cells with a process for producing cement.

FIG. 19 schematically shows an example of integration of moltencarbonate fuel cells with a process for producing iron or steel.

FIG. 20 shows process flows for an example of integration of moltencarbonate fuel cells with a process for producing iron or steel.

FIG. 21 schematically shows an example of a system for generatinghydrogen and electrical power in a refinery setting.

FIG. 22 shows an example of process flows in a system for generatinghydrogen and electrical power in a refinery setting.

FIG. 23 schematically shows an example of a system for generatinghydrogen and electrical power in a refinery setting.

FIG. 24 shows an example of process flows in a system for generatinghydrogen and electrical power in a refinery setting.

FIG. 25 schematically shows an example of a configuration for generatingelectricity.

FIG. 26 shows results of simulations of a system for generatingelectricity.

DETAILED DESCRIPTION OF THE EMBODIMENTS Overview

In various aspects, the operation of molten carbonate fuel cells can beintegrated with a variety of chemical and/or materials productionprocesses. The production processes can correspond to production of anoutput from the molten carbonate fuel cells, or the production processcan consume or provide one or more fuel cell streams.

Integration with Fischer-Tropsch Synthesis

In various aspects, systems and methods are provided for producinghigh-quality products from Fischer-Tropsch synthesis based on reactionof syngas produced from a MCFC system. The systems and methods canoptionally but sometimes preferably use a non-shifting Fischer-Tropschcatalyst, such as a cobalt-based catalyst, to produce largely saturatedparaffins of high average molecular weight. This can sometimes bereferred to as “low-temperature” Fischer-Tropsch synthesis.Alternatively, the systems and methods can optionally but sometimespreferably use a shifting Fischer-Tropsch catalyst, such as aniron-based catalyst. This can sometimes be referred to as“high-temperature” Fischer-Tropsch synthesis. While other catalystsystems and process conditions may be employed, typical commercialoperations can utilize a catalyst based on either cobalt or iron. Insome preferred aspects, the largely saturated paraffins typically formedin Fischer-Tropsch product streams can be processed into high-valueproducts such as diesel fuel, jet fuel, and lubricants, and/or can beutilized as blending stocks for those products. In some aspects, thesystems and methods can more efficiently produce these products whilealso producing substantial amounts of electrical power, for instance forthe Fischer-Tropsch process and/or for export, while also makingefficient use of the carbon input to the overall process. The system canprovide high total efficiency in terms of the sum of the electrical andchemical outputs relative to the inputs. Additionally or alternately,the system can produce a CO₂ stream (or one or more CO₂ streams)suitable for carbon capture/sequestration.

Syngas can be utilized to make variety of products and components usefulin the production of fuels, lubricants, chemicals, and/or specialties.One process for converting syngas to these products includes theFischer-Tropsch process, in which syngas can be reacted over a catalystat elevated temperature and pressure to produce long-chain hydrocarbons(or hydrocarbonaceous compounds) and oxygenates. The most commoncatalysts utilized can typically include iron-based catalysts (forso-called high-temperature-Fischer-Tropsch synthesis) and cobalt-basedcatalysts (for so-called low temperature-Fischer-Tropsch synthesis).Iron-based catalysts, along with other related catalysts, can also bereferred to as shifting catalysts, as the water-gas shift reaction cantend to be readily equilibrated on these catalysts. Cobalt-containingcatalysts and other related catalysts can be referred to asnon-shifting, as they do not appear to substantially perform and/orcatalyze the water-gas shift equilibration reaction at standardoperating conditions.

Examples of suitable Fischer-Tropsch catalysts can generally include asupported or unsupported Group VIII, non-noble metal e.g., Fe, Ni, Ru,and/or Co, with or without a promoter e.g., ruthenium, rhenium, and/orzirconium. These Fischer-Tropsch processes can typically include fixedbed, fluid bed, and/or slurry hydrocarbon synthesis. In some aspects, apreferred Fischer-Tropsch process can be one that utilizes anon-shifting catalyst, such as based on cobalt and/or ruthenium,preferably comprising at least cobalt, and preferably a promoted cobalt,with the promoter comprising zirconium and/or rhenium, preferably beingrhenium, although other promoter metals may also be used. The activitiesof these catalysts can be enhanced by the addition, optionally as partof a catalyst support, of a variety of metals, including copper, cerium,rhenium, manganese, platinum, iridium, rhodium, molybdenum, tungsten,ruthenium or zirconium. Such catalysts are well known, and a preferredcatalyst is described in U.S. Pat. No. 4,568,663 as well as EuropeanPatent No. 0 266 898. The synthesis gas feed used in typicalFischer-Tropsch processes can comprise a mixture of H₂ and CO whereinH₂:CO are present in a ratio of at least about 1.7, preferably at leastabout 1.75, more preferably 1.75 to 2.5, such as at least about 2.1and/or about 2.1 or less.

Fischer-Tropsch processes can be implemented in a variety of systemssuch as fixed bed, slurry bed, and multiple channel designs. In variousaspects, Fischer-Tropsch processes can be employed in a wide variety ofreactors, such as small reactors (e.g. 1+ barrel/day) or in very largereactors (e.g. 10,000-50,000 barrels/day or more). The product,typically a hydrocarbon wax, can be used as is and/or can be convertedto other (e.g. liquid) components by a variety of well-known chemicalprocesses.

Generally, the Fischer-Tropsch process can be operated in thetemperature range of about 150° C. to about 32° C. (302° F.-626° F.) andat pressures ranging from about 100 kPaa to about 10 MPaa. Modifying thereaction conditions within the Fischer-Tropsch process can providecontrol over the yield and/or composition of the reaction products,including at least some control of the chain length of the reactionproducts. Typical reaction products can include alkanes (primaryreaction product), as well as one or more of oxygenates, olefins, otherhydrocarbonaceous compounds similar to hydrocarbons but which maycontain one or more heteroatoms different from carbon and hydrogen, andvarious additional reaction by-products and/or unreacted feedcomponents. These additional reaction products and feed components caninclude H₂O, unreacted syngas (CO and/or H₂), and CO₂, among otherthings. These additional reaction products and unreacted feed componentscan form a tail gas that can be separated from the primary reactionproducts of the Fischer-Tropsch process in gaseous form, as opposed tonon-gaseous product, such as the more typical (desired) liquids and/orhydrocarbonaceous compounds generated by the process. When the goal ofthe Fischer-Tropsch process is synthesis of longer chain molecules, suchas compounds suitable for use as a naphtha feed, a diesel feed, or otherdistillate boiling range molecules, some small (C1-C4) alkanes, olefins,oxygenates, and/or other hydrocarbonaceous compounds may be incorporatedinto the tail gas. The primary products from Fischer-Tropsch synthesiscan be used directly, and/or can undergo further processing, as desired.For example, a Fischer-Tropsch synthesis process for forming distillateboiling range molecules can generate one or more product streams thatcan subsequently be dewaxed and/or hydrocracked in order to generatefinal products, e.g. with desired chain lengths, viscosities, and coldflow properties.

Integration of a Fischer-Tropsch process with molten carbonate fuelcells can allow for integration of process streams between the synthesisprocess and the fuel cell. The initial syngas input for theFischer-Tropsch process can be generated by the reforming stageassociated with the fuel cell. Additionally or alternately, the tail gasproduced by the Fischer-Tropsch process can be recycled to provide asupplemental fuel stream for the anode of the fuel cell, and/or toprovide a source of CO₂ for the fuel cell cathode. TheMCFC/Fischer-Tropsch system can further additionally or alternately beintegrated with the use of a gas turbine power plant and carbon capture,providing an overall plant producing larger amounts of electricity andliquid fuels.

In some aspects, the tail gas produced by a Fischer-Tropsch process canbe used in an improved manner to provide at least a portion of the CO₂for a cathode inlet stream. The tail gas from a Fischer-Tropschsynthesis reaction can generally be considered a relatively low valuestream. The tail gas can include a substantial portion of CO₂, and canpotentially include at least some fuel components such as CO, H₂, smallalkanes, and/or small oxygenates. Due to the relatively lowconcentration of the fuel components and/or the relatively highconcentration of the CO₂, the tail gas is generally not useful directlyas a fuel. A separation can be performed to attempt to remove the fuelcomponents from the tail gas, but such a separation can typically beinefficient relative to the amount of fuel derived from the separation.

Instead of attempting to separate the fuel components from the tail gasstream, in various aspects, a separation can be performed to separate aportion of the CO₂ from the tail gas stream. This can result information of a CO₂ stream and a remaining portion of the tail gasstream. This separation strategy can potentially provide severalpotential benefits. When the separation is done to isolate only aportion of the CO₂, the separation can preferably be used to form arelatively high purity CO₂ stream. Although the concentration of fuel inthe remaining tail gas stream may be only moderately increased, thetotal volume of the tail gas stream can be reduced, making the remainingportion of the tail gas stream more suitable for use as at least aportion of a cathode inlet stream, or possibly using the remainingportion as the cathode inlet stream. Prior to use as a cathode inletstream, the fuel in the remaining portion of the tail gas can becombusted to form CO₂ and H₂O, optionally while also heating theremaining portion of the tail gas to a desired cathode inlettemperature. It is noted that one option for controlling the temperatureof the remaining portion of the tail gas stream after combustion caninclude controlling the amount of CO₂ removed during the separation.This type of separation strategy can allow the fuel in the tail gas tobe used efficiently without having to perform a separation to isolatethe fuel. Additionally, when only a partial separation is performed onthe CO₂ in the tail gas, a relatively purer CO₂ stream can be generated.Such a relatively pure CO₂ stream can be suitable for sequestration orfor other uses involving high purity CO₂.

In some aspects, integration of a Fischer-Tropsch process with a MCFCcan enable a different type of process flow than a conventional processthat utilizes, for example, a steam reformer or autothermal reformer. Atypical syngas output from an autothermal reformer can have a H₂:COratio of less than about 2:1. As a result, to the degree thatmodification of the ratio of H₂ to CO is desired for a conventionalprocess, the modification can typically correspond to increasing theamount of H₂ relative to the amount of CO, e.g., to about 2:1. Bycontrast, in various aspects the composition of the anode exhaust from aMCFC can have a H₂:CO ratio of at least about 2.5:1, such as at leastabout 3:1. In some aspects, it may be desirable to form a syngas with aratio of H₂:CO of about 2:1, such as a ratio of at least about 1.7, orat least about 1.8, or at least about 1.9, and/or about 2.3 or less, orabout 2.2 or less, or about 2.1 or less. In such aspects, in order toachieve the desired ratio, the amount of H₂ can be reduced relative tothe amount of CO. This can be accomplished using a reverse water gasshift reaction, using a membrane to separate out a (high purity) H₂stream, or by any other convenient method of modifying the ratio ofH₂:CO.

Fischer-Tropsch synthesis can benefit from a number of features of aMCFC system. Typically, syngas produced by Fischer-Tropsch from methanecan be made via steam-reforming, autothermal reforming, or partialoxidation involving the use of methane reacted with purified oxygen fromair. Such systems can require substantial amounts of capital equipment(air separator) and must also utilize various steps for pre- andpost-gas cleanup to produce a syngas of the correct H₂/CO ratio, whichalso needs to be free from undesirable impurities. This can beespecially true of the more productive Co-catalyst-based (non-shifting)systems, which are sensitive to poisons such as sulfur. Fischer-Tropschsystems can require substantial heat management and/or heat exchange andcan take place at relatively high temperatures.

The MCFC system, in the process of making electricity, can performsyngas production and can produce a clean syngas as a consequence of thelarge amount of catalyst located in the anode (typically Ni-based) whichcan tolerate and/or remove most Fischer-Tropsch poisons. As a result,gas processing, heat exchange, and/or cleanup can be at least partiallyperformed in the MCFC. In addition, it can be relatively easy to achievea desired H₂/CO ratio, as the anode effluent has sufficient amounts ofall four water-gas shift components and can be adjusted simply by acombination of water and/or CO₂ removal and/or additional WGS (orreverse shift).

Fischer-Tropsch reactors can typically produce large amounts of steam,due to the exothermic nature of the reaction. Use of the steamproductively can be difficult depending on the plant location. Whencoupled to an MCFC system that produces electricity, the system canoffer a number of areas where heat integration can use theFischer-Tropsch excess steam/heat. Potential integration examples caninclude heating reactants after removal of CO₂ (such as after cryogenicremoval), heating incoming cathode oxidant (air) if it comes from a lowtemperature CO₂ source, and/or integration into a heat-recoverysteam-generation system already present for combined cycle electricalgeneration from the MCFC.

Fischer-Tropsch processes can usually make a quantity of C1 to C4hydrocarbons (possibly including C1 to C4 oxygenates) not readilyincorporated into liquid products. Such C1 to C4 hydrocarbons and/oroxygenates can be recycled to the MCFC either directly or with apre-reformer and can be used to make electrical power and/or to recyclesyngas.

For installations where the use of CO₂ has additional value, theseparation of CO₂ captured from the anode exhaust can provide additionalopportunities for integration. Such CO₂ can be used, for example forsecondary oil recover, for re-injection into the well, or in otherprocesses that where it can be repurposed instead of being wasted inatmospheric exhaust, while enhancing the overall system.

The anode input for a combined Fischer-Tropsch Molten Carbonate FuelCell (FT-MCFC) system can comprise or be a fresh methane feed, anothertype of hydrocarbon or hydrocarbonaceous feed, a feed based on one ormore recycle streams containing one or more of CO, CO₂, H₂, and lighthydrocarbons from the Fischer-Tropsch reactor and/or from subsequentprocessing steps, or a combination thereof. Preferably, the anode feedcan comprise or be natural gas and/or methane. The anode outlet from theMCFC system can be used directly, or more commonly can undergo a varietyof processes to adjust the H₂/CO ratio and/or to reduce the water andCO₂ content, so as to be optimized for Fischer-Tropsch synthesis. Suchadjustment processes may include separation, water-gas shift reaction,condensation, and absorption, and the like, as well as combinationsthereof.

The cathode inlet can contain CO₂ and may be derived from a separatecombustion process, if present (e.g. from a gas turbine and/or other CO₂effluent). Additionally or alternately, the cathode inlet mayadditionally or alternately be generated at least in part by recycle ofstreams from the MCFC anode (after separation) and/or by recycle fromthe Fischer-Tropsch processes. Further additionally or alternately, thecathode inlet stream can contain CO₂ derived from the tail gas from theFischer-Tropsch process. Still further additionally or alternately, thecathode inlet may be partly derived from combustion of fresh methane orhydrocarbon feed. The cathode effluent can typically be exhausted to theatmosphere, optionally but preferably after heat recovery to, forexample, provide heat for other process streams and/or in combined cycleelectrical production, though the cathode effluent could optionally butless preferably be sent for further treatment, if desired.

The MCFC fuel utilization conditions can be adjusted to provide adesired amount of electrical energy relative to syngas output. Forapplications where there are substantial electrical needs (for example,a small gas production alongside a very large off-shore crude oilplatform), the FT-MCFC system may produce proportionally more electricalpower. Operations based on large-scale conversion, where substantialinfrastructure is present, can produce a variety of electrical/chemicalmixtures and may vary the output based on local needs.

FIG. 6 schematically shows an example of integration of molten carbonatefuel cells (such as an array of molten carbonate fuel cells) with areaction system for performing Fischer-Tropsch synthesis. In FIG. 6,molten carbonate fuel cell 610 schematically represents one or more fuelcells (such as fuel cell stacks or a fuel cell array) along withassociated reforming stages for the fuel cells. The fuel cell 610 canreceive an anode input stream 605, such as a reformable fuel stream, anda CO₂-containing cathode input stream 609. The cathode output from fuelcell 610 is not shown in FIG. 6. The anode output 615 from fuel cell 610can then, optionally but preferably, be passed through one or moreseparation stages 620, which can include CO₂, H₂O, and/or H₂ separationstages, and/or one or more water gas shift reaction stages, in anydesired order, as described below and as further exemplified in FIGS. 1and 2. Separation stages can produce one or more streams correspondingto a CO₂ output stream 622, H₂O output stream 624, and/or H₂ outputstream 626. The separation stages can also produce a syngas output 625suitable for use as an input for Fischer-Tropsch reaction stage 630.

In the scheme shown in FIG. 6, the anode outlet can produce a syngaswith relatively large amounts of water and CO₂, as well as exhibiting aH₂:CO ratio higher than the preferred 2:1 ratio. In a series of steps,the stream can be cooled to remove water, then passed through a CO₂separation stage to remove most of the CO₂. The anode outlet streamand/or the resulting effluent can have a relatively high H₂:CO ratio(typically from about 2.5 to about 6:1, for example from about 3:1 toabout 5:1) and enough CO₂ to provide reactant for the reverse water gasshift reaction. The anode outlet stream and/or the resulting effluentcan then be heated to a relatively high temperature (typically fromabout 400° C. to about 550° C.) where CO₂ can react with H₂ to produceCO+H₂O. The resultant gas can exhibit a H₂:CO ratio closer to theconventional 2:1. This gas can then be fed into the Fischer-Tropschreactor containing a non-shifting Fischer-Tropsch catalyst. As analternative, from an energy management standpoint, it may be desirableto perform the reverse water gas shift reaction first, and then separateout CO₂ and H₂O in a convenient order.

The Fischer-Tropsch reaction stage 630 can produce a Fischer-Tropschproduct 635 that can be used directly or that can undergo furtherprocessing, such as additional hydroprocessing. Hydroprocessing of theFischer-Tropsch wax, when desired, can typically be accomplished atelevated temperature and pressure in the presence of hydrogen to producematerials (such as at least one non-gaseous product) that can be usefulproducts such as diesel blending stock and/or lube base stock.Fischer-Tropsch reaction stage 630 can additionally or alternatelygenerate a tail gas 637 that can optionally be recycled for use as arecycled fuel 645, for instance for the anode and/or cathode portion ofthe fuel cell 610. In most cases, it can be preferable to recycle thisstream at least to the cathode where the residual fuel components (CO,H₂, and light hydrocarbons) can be mixed and burned with oxidant (air)to reach an appropriate temperature for the cathode input. Optionally,the CO₂ output 622 from the separation stage(s) 620 can be used as atleast a portion of the input (not shown) for the cathode of fuel cell610, though this is generally not preferred.

In most embodiments, the syngas output from a MCFC system can beutilized as the source of syngas for a Fischer-Tropsch process. In thecase of shifting FT catalysts (such as an Fe-based catalyst), theshifting catalyst can adjust the H₂/CO ratio, even if different than theconventional 2:1, via the water-gas shift reaction (or reverse water gasshift reaction) under reaction conditions to produce Fischer-Tropschproducts. While a lower H₂:CO ratio can be desired in certainembodiments, individual systems could choose to adjust or not to adjustthis ratio prior to exposure to a shifting catalyst. In some aspects,removal of CO₂ prior to introducing can be reduced or minimized whenusing a shifting catalyst. When using a Fischer-Tropsch synthesiscatalyst based on cobalt (or another type of non-shifting catalyst), thesynthesis catalyst typically does not have meaningful activity forperforming the water gas shift reaction at Fischer-Tropsch reactionconditions. As a result, CO₂ present in a syngas stream exposed to anon-shifting Fischer-Tropsch catalyst can act mainly as a diluent, andtherefore may not substantially interfere with the Fischer-Tropschreaction, though it can tend to lower reactor productivity due todilution. However, due to the non-shifting nature of the catalyst, thecatalyst cannot easily adjust the ratio of H₂:CO of the syngas thatenters the Fischer-Tropsch reactor.

FIG. 7 schematically shows another example of integration of moltencarbonate fuel cells (such as an array of molten carbonate fuel cells)with a reaction system for performing Fischer-Tropsch synthesis. Theconfiguration shown in FIG. 7 can be suitable, for example, for use in alarger scale system. In FIG. 7, molten carbonate fuel cell 710schematically represents one or more fuel cells (such as fuel cellstacks or a fuel cell array) along with associated reforming stages forthe fuel cells. The fuel cell 710 can receive an anode input stream 705,such as a reformable fuel stream, and a CO₂-containing cathode inputstream 709. The cathode input stream 709 can correspond to an exhaustgas from a combustion-powered turbine, to a recycle stream from anothergas stream in the integrated Fischer-Tropsch/MCFC system, to a methanestream that has been combusted to generate heat, and/or to anotherconvenient stream that can provide CO₂ at a desired temperature for thefuel cell. The cathode input stream 709 can typically include a portionof an oxygen-containing stream. The anode output 715 from fuel cell 710can be initially passed through a reverse water gas shift stage 740 tomodify the ratio of H₂:CO in the anode exhaust. The modified anodeexhaust 745 can then be passed into one or more separation stages 720,which can include CO₂ and H₂O separation stages. Separation stages canproduce one or more streams corresponding to a CO₂ output stream 722and/or an H₂O output stream 724. Optionally but preferably, the outputfrom the separation stage(s) for use in the Fischer-Tropsch process canhave a CO₂ concentration that is less than half of a CO₂ concentrationof the anode exhaust, a H₂O concentration that is less than half of aH₂O concentration of the anode exhaust, or a combination thereof. Acompressor (not shown) can be used after some or all of the separationstages 720 to achieve a desired input pressure for the Fischer-Tropschreaction process. Optionally, an H₂ output stream (not shown) couldadditionally or alternately be generated. The separation stages cantypically produce a syngas output 725, which can be suitable for use asan input for Fischer-Tropsch reaction stage 730, such as a non-shiftingFischer-Tropsch synthesis catalyst. The Fischer-Tropsch reaction stage730 can produce Fischer-Tropsch liquid products 735, lower boiling C2-C4compounds 732, and a tail gas 737. The lower boiling C2-C4 compounds canbe separated from the liquid products and then further isolated for useas products and/or raw materials for further reaction. Additionally oralternately, the C2-C4 compounds can be allowed to remain with the tailgas 737 and can be recycled, for example, to the cathode aftercombustion to provide heat and CO₂ for the fuel cell cathode.

Example of Integration Application—Distributed Processing

For some Fischer-Tropsch applications, such as those in isolated areas,a combined FT-MCFC system can have an advantage of being sized toprovide at least a portion of the local electrical power to operate thesystem, and additionally or alternately to provide additional power forother facilities or a locality, while converting additional hydrocarboninputs beyond this requirement into higher value products. The powerprovided can be a portion of the power or all of the necessary power forthe system and/or a locality. Such installations could include isolatedland-based gas sources, ship- and/or platform-mounted sea-basedinstallations, or the like. Due to the ease of adjusting the size of theMCFC system, based on the size and number of fuel cell stacks or arrays,any conceivable scale from very small to world-scale installations canbe integrated.

Fischer-Tropsch synthesis has traditionally been most practical whendone at very large scale. This has been primarily due to the economiesof scale of several of the core processes including air separation,reforming of methane to syngas (for example, by auto-thermal reforming,catalytic partial oxidation, or the like), and the hydrocarbon synthesisreactor. Conventionally, single process “trains” can produce greaterthan 10,000 barrels of product/day, and overall plant sizes from 30-150thousands of barrels/day have been practiced commercially. Foroperations of this size, very large gas deposits were required, and thishas limited the applications of the technology, at economicallyreasonable terms, to only a few gas reservoirs.

In contrast to such conventional large scale operations, in someaspects, a process and system are provided for using Fischer-Tropschsynthesis in an efficient system that can be applied advantageously tosmaller gas deposits. The process and system can employ a MCFC toproduce syngas to feed the Fischer-Tropsch reactor and need notnecessarily include many of the complexities of a conventionallarge-scale plant. The MCFC system can be capable of producing at leasta portion (and potentially all) of the electrical power for the varioussub-systems, such as compressors and pumps, while producing a very highcarbon conversion from syngas to liquid products. It can be used witheither shifting or non-shifting catalysts in various configurations andcan be suitable to either high- or low-temperature Fischer-Tropschprocesses.

As noted above, examples of suitable Fischer-Tropsch catalysts cangenerally include a supported or unsupported Group VIII, non-noble metale.g., Fe, Ni, Ru, and/or Co, with or without a promoter e.g., ruthenium,rhenium, and/or zirconium. These Fischer-Tropsch processes can bepracticed using reactors such as fixed bed, fluid bed, and/or slurryhydrocarbon synthesis. Some Fischer-Tropsch processes can utilize anon-shifting catalyst, such as based on cobalt and/or ruthenium,preferably comprising at least cobalt, and preferably a promoted cobalt,with the promoter comprising or being zirconium and/or rhenium,preferably comprising or being rhenium. Such catalysts are well known,and a preferred catalyst is described in U.S. Pat. No. 4,568,663 as wellas European Patent No. 0 266 898, both of which are hereby incorporatedby reference for their description of such catalyst and itsphysico-chemical characteristics. The synthesis gas feed used in theFischer-Tropsch process can comprise a mixture of H₂ and CO whereinH₂:CO are present in a ratio of at least about 1.7, preferably at leastabout 1.75, more preferably 1.75 to 2.5, such as at least about 2.1and/or about 2.1 or less. For non-shifting catalysts, the syngasproduced by the MCFC can typically start with a H₂:CO ratio well above2:1, and additional processes can be used to “shift” the syngas mixturecloser to the conventional H₂:CO ratio of about 2:1.

Alternately, a shifting catalyst (such as an Fe-based catalyst) can beused. While the product distribution and overall productivity ofshifting catalysts can sometimes be considered inferior to non-shiftingsystems, shifting catalyst based systems can have the distinct advantageof being able to employ a wider range of syngas mixtures (having a widerrange of H₂:CO ratios). Conventionally, shifting catalysts have beenused primarily to accommodate coal-sourced syngas having a H₂:CO ratiotypically from about 0.7 to about 1.5. In contrast, the syngas mixtureemployed herein can contain excess H₂, but also can contain a largepercentage of CO₂. A system incorporating a shifting catalyst canadvantageously “reverse-shift” these mixtures, reacting H₂ with CO₂ toproduce additional CO for the Fischer-Tropsch reactor, in someembodiments without needing to pre-shift the reactants to approximatelya 2:1 H₂:CO ratio.

In a distributed processing environment, a Fischer-Tropsch process canbe operated in the temperature range of about 150° C. to about 33° C.(about 302° F. to about 626 F) and at pressures ranging from about 100kPaa to about 10 MPaa (about 1 bara to about 100 bara). Modifying thereaction conditions of the Fischer-Tropsch process can provide controlover the yield and composition of the reaction products, including atleast some control of the chain length of the reaction products. Typicalreaction products can include alkanes (primary reaction product), aswell as one or more of oxygenates, olefins, other hydrocarbonaceouscompounds similar to hydrocarbons but that may contain one or moreheteroatoms different from carbon or hydrogen, and/or various additionalreaction by-products and/or unreacted feed components. These additionalreaction products and feed components, when present, can include one ormore of H₂O, unreacted syngas (CO and/or H₂), CO₂, and N₂. Theseadditional reaction products and unreacted feed components canadditionally or alternately form a tail gas that can be separated fromthe primary reaction products of the Fischer-Tropsch process. When thegoal of the Fischer-Tropsch process is synthesis of longer chainmolecules, such as compounds suitable for use as a naphtha feed, adiesel feed, and/or other distillate boiling range molecules, some small(C1-C4) alkanes, olefins, oxygenates, and/or other hydrocarbonaceouscompounds may be incorporated into the tail gas. The primary productsfrom Fischer-Tropsch synthesis can be used directly, and/or can undergofurther processing. For example, a Fischer-Tropsch synthesis process forforming distillate boiling range molecules can generate one or moreproduct streams that can be subsequently dewaxed and/or hydrocracked inorder to generate final products with desired chain lengths,viscosities, and cold flow properties.

Under typical operating conditions, representative gas compositions atthe MCFC anode exhaust can have H₂:CO ratios that can range from about2.5:1 to about 10:1 and that can, in most embodiments, fall in the rangefrom about 3:1 to about 5:1. This anode exhaust composition can alsocontain significant amounts of both water and CO₂.

An integrated MCFC-FT system can allow for any one or more of severalalternate configurations that may be used advantageously, avoidingprocesses typical of conventional Fischer-Tropsch. In an aspect withsome similarities to a conventional configuration, the syngas from theanode exhaust can be shifted close to a 2:1 H₂:CO ratio (e.g., fromabout 2.5:1 to about 1.5:1, from about 1.7:1 to about 2.3:1, from about1.9:1 to about 2.1:1, from about 2.1:1 to about 2.5:1, or from about2.3:1 to about 1.9:1) and most (at least half) of the CO₂ and H₂O can beremoved. Alternately, in another configuration, the syngas from theanode exhaust can be used as is, without any change in composition, butwith simple adjustment of temperature and pressure to the appropriateFischer-Tropsch catalyst conditions. In still another configuration, thesyngas from the anode exhaust can be used without being (water gas)shifted, but water can be condensed and largely removed, producing asyngas comprising H₂, CO, and CO₂, with small amounts (typically <5%) ofother gasses. In yet another configuration, water can optionally beremoved and then the syngas from the anode exhaust can be reacted in awater-gas shift reactor to “reverse” the shift process, thus convertingmore CO₂ to CO and rebalancing the H₂:CO ratio closer to about 2:1(e.g., from about 2.5:1 to about 1.5:1, from about 1.7:1 to about 2.3:1,from about 1.9:1 to about 2.1:1, from about 2.1:1 to about 2.5:1, orfrom about 2.3:1 to about 1.9:1). In an alternate configuration, theshifting process can be followed by, or can precede, separation of someCO₂ to provide CO₂ for carbon capture and/or to reduce CO₂ dilution inthe syngas from the anode exhaust.

In conventional Fischer-Tropsch processes, the tail gas containingunreacted syngas, along with methane and other C1-C4 gases, canrepresent unused reactants and low value products. For very large scaleinstallations, these light gases may justify additional processing (e.g.cracking the C2 and C3 molecules to olefins for plastics, recovery ofliquefied propane gas or butane, or the like). Unconverted syngas andmethane can be recycled to the Fischer-Tropsch synthesis reactor,representing efficiency losses and loss of reactor throughput. In adistributed system environment, some or all lighter gases not convertedto product liquids can be used more advantageously as feed for the anodeof the fuel cell and/or can be used more advantageously to provide asource of CO₂ for the fuel cell cathode.

In one example of a process flow for a MCFC-FT system in a distributedenvironment, the anode exhaust from a MCFC can be used as the input tothe Fischer-Tropsch reaction system after a reduced or minimized amountof processing. If the Fischer-Tropsch catalyst is a shifting catalyst,the anode exhaust can be compressed to a pressure suitable for theFischer-Tropsch reaction. The compression process may coincidentallyand/or purposefully result in some separation/removal of water. If theFischer-Tropsch catalyst is a non-shifting catalyst, an additionalreverse water gas shift reaction can be performed, typically prior tocompression, to adjust the syngas H₂:CO ratio in the anode exhaust.Optionally, a hydrogen-permeable membrane, other gas-permeable membrane,or other separation technique could be used in addition to or in placeof the reverse water gas shift reaction to separate out a (high purity)H₂ stream as part of adjusting the H₂:CO ratio in the anode exhaust.Otherwise, additional separations and/or modification of the anodeexhaust can be avoided, allowing the anode exhaust to be used in theFischer-Tropsch system with minimal processing. Because the anodeexhaust can have a substantial content of CO₂, reducing or minimizingthe number of separations and/or modifications prior to using a portionof the anode exhaust as the input for a Fischer-Tropsch process canresult in having a Fischer-Tropsch input stream that also can contain asubstantial content of CO₂. For example, the concentration (such as involume percent) of CO₂ in the Fischer-Tropsch input stream can be atleast about 60% of the concentration in the anode exhaust, or at leastabout 65%, or at least about 70%, or at least about 75%, or at leastabout 80%, or at least about 85%, or at least about 90%. Due to the CO₂content of an anode exhaust from a MCFC, as well as the tendency for theFischer-Tropsch system to independently generate a substantial amount ofCO₂, there can be quite a considerable concentration of CO₂ in theFischer-Tropsch product effluent. This CO₂ can be at least partiallyseparated from the other products of the Fischer-Tropsch system forsequestration/capture, further processing, and/or use in one or moreother processes.

FIG. 8 schematically shows an example of integration of molten carbonatefuel cells (such as an array of molten carbonate fuel cells) with areaction system for performing Fischer-Tropsch synthesis. Theconfiguration in FIG. 8 can be suitable for use in a small scale orother distributed environment setting. In FIG. 8, molten carbonate fuelcell 810 schematically represents one or more fuel cells (such as fuelcell stacks or a fuel cell array) along with associated reforming stagesfor the fuel cells. The fuel cell 810 can receive an anode input stream805, such as a reformable fuel stream, and a CO₂-containing cathodeinput stream 809. The anode output 815 can be passed through an optionalreverse water gas shift stage 840. For example, if Fischer-Tropschreaction stage 830 includes a shifting catalyst, the water gas shiftstage 840 can be omitted. The optionally shifted anode exhaust 845 canthen be passed into a compressor 860 to achieve a desired input pressurefor the Fischer-Tropsch reaction stage 830. Optionally, a portion of thewater present in the optionally shifted anode exhaust 845 can be removed864, prior to, during, and/or after compression 860. The Fischer-Tropschreaction stage 830 can produce a Fischer-Tropsch product 835 that can beused directly or that can undergo further processing, such as additionalhydroprocessing. Fischer-Tropsch reaction stage 830 can also generate atail gas 837 that can be recycled for use as a recycled fuel 845 for thecathode portion of the fuel cell 810. Prior to recycle, at least aportion 862 of the CO₂ present in the tail gas 837 can be separated fromthe tail gas. Alternatively, the separation of CO₂ can be performedprior to, during, and/or after the separation of Fischer-Tropsch product835 from the tail gas 837.

Example 1—Integration of MCFC with Small Scale FT Processing System

This example describes operation of a small scale Fischer-Tropschprocess integrated with operation of an MCFC to provide the syngas inputfor the Fischer-Tropsch process. The Fischer-Tropsch process in thisexample can generate about 6000 barrels per day of Fischer-Tropschliquid products. The configuration for integrating the MCFC with theFischer-Tropsch process in this example was a variation on theconfiguration shown in FIG. 8. Thus, in this example, a reduced orminimized amount of separations or modifications can be performed on theanode exhaust prior to introducing the anode exhaust to theFischer-Tropsch process. In this example, simulation results are shownfor both the case where CO₂ was separated from the Fischer-Tropsch tailgas for capture and the case where capture was not performed. In thisexample, the anode input comprised fresh methane, such as methane from asmall local source. The cathode input in this example was based on useof combustion of the tail gas to form a cathode input, optionally afterseparation of CO₂ for sequester. However, the cathode input can beprovided by any convenient source.

FIG. 9 shows results from simulations performed under several differentsets of conditions. In FIG. 9, the first two columns show simulationresults from use of a Co-based (non-shifting) catalyst for theFischer-Tropsch reaction, while the third and fourth columns showresults from use of a Fe-based (shifting) catalyst. For the Co-basedcatalyst, an additional “reverse” water gas shift was performed on theanode output stream to reduce the H₂:CO ratio to a value closer to thedesired 2:1 ratio. This additional shift reaction was not performed onthe anode output prior to introducing the portion of the anode outputstream into the Fischer-Tropsch system when using the Fe-based catalyst.The first and third columns show simulation results from a systemwithout CO₂ capture, while the second and fourth columns show simulationresults from a system where CO₂ was separated from the Fischer-Tropschtail gas for sequester. The amount of CO₂ removed was selected to becomparable for the second and fourth columns while still providingsufficient CO₂ in the cathode to maintain at least a ˜1% CO₂ content inthe cathode exhaust. In all of these simulations, the fuel utilizationin the anode was about 35%. About 40% of the methane was reformed in thefuel cell, with the remainder of the methane being reformed in anearlier integrated reforming stage. The steam to carbon ratio in theanode feed was about 2. The row corresponding to power from a steamturbine represents additional power generated by heat recovery from thecathode exhaust.

Unlike a steam reformer, an MCFC can generate electrical power whilealso reforming fuel and assisting with separation of CO₂ from thecathode input stream. As a result, even for a small scale FischerTropsch system, the integrated MCFC-FT system can provide reasonable netefficiencies relative to the input carbon amounts. As shown in FIG. 9,relative to the net carbon input to the burner(s) for heating the systemand the fuel cell anode, the total plant efficiency of production ofFischer-Tropsch liquids was between about 60% and about 70%, such as atleast about 63%. The total plant efficiency represents an efficiencybased on the combined electrical and chemical (Fischer-Tropsch liquidproducts) output of the plant relative to the total inputs.

Example 2—Integration of MCFC with a FT Processing System

This example describes operation of a Fischer-Tropsch process integratedwith operation of an MCFC to provide the syngas input for theFischer-Tropsch process. A combustion turbine was also integrated withthis process via using the exhaust from the turbine as the input to thecathode of the MCFC. The configurations for integrating the MCFC withthe Fischer-Tropsch process were variations on the configuration shownin FIG. 7. In this example, results are shown for a first configurationwhere CO₂ was separated from the anode exhaust prior to input to theFischer-Tropsch process, and for a second configuration where CO₂ wasinstead separated from the Fischer-Tropsch tail gas. Both configurationsused a non-shifting catalyst, so a reverse water gas shift was performedin both simulations to adjust the H₂:CO ratio. In this example, theanode input comprised fresh methane.

FIG. 10 shows results from the simulations that were performed. In thesimulations shown in FIG. 10, a fuel utilization of about 30% was usedfor the fuel cells. The total efficiency in terms of combined electricalpower generation and generation of Fischer-Tropsch products was about61%, which was similar to the efficiency for the simulations fromExample 1. However, about 40% of the total efficiency corresponded toelectrical power generation in this example.

Integration with Production of Methanol Intermediate and Final Products

Methanol can typically be made from a syngas mixture, such as a mixtureincluding CO, H₂, and optionally CO₂, at high pressure and temperature.Conventionally, the majority of methanol plants can utilize natural gasas a feedstock and can generate syngas by common processes like steamreforming, auto-thermal reforming, or partial oxidation. Most commonconfigurations utilize a catalyst that can produce relatively lowconversion per pass and can involve substantial recycle, along withproduction of various off-gasses and purge streams.

Integration of methanol synthesis with a molten carbonate fuel cell canallow for new configurations designed for higher efficiency and/or loweremissions. During methanol synthesis, carbon monoxide and hydrogen canreact over a catalyst to produce methanol. Commercial methanol synthesiscatalysts can be highly selective, with selectivities of greater than99.8% possible under optimized reaction conditions. Typical reactionconditions can include pressures of about 5 MPa to about 10 MPa andtemperatures of about 250° C. to about 300° C. With regard to the syngasinput for methanol synthesis, the preferred ratio of H₂ to CO (about 2:1H₂:CO) does not match the typical ratio generated by steam reforming.However, catalysts that facilitate methanol formation from syngas cansometimes additionally facilitate the water-gas shift reaction. As aresult, the reaction scheme below shows that CO₂ can also be used toform methanol:2H₂+CO=>CH₃OH3H₂+CO₂=>CH₃OH+H₂O

For methanol synthesis reactions, the composition of the synthesis gasinput can be characterized by the Module value M:M=[H₂−CO₂]/[CO+CO₂]

Module values close to 2 can generally be suitable for production ofmethanol, such as values of M that are at least about 1.7, or at leastabout 1.8, or at least about 1.9, and/or less than about 2.3, or lessthan about 2.2, or less than about 2.1. As can be noted from the ModuleValue equation above, in addition to the ratio of H₂ to CO, the ratio ofCO to CO₂ in the syngas can impact the reaction rate of the methanolsynthesis reaction.

During operation, a molten carbonate fuel cell can transfer CO₂ from thecathode side of the fuel cell to the anode side as part of the internalreaction that allows for generation of electricity. Thus, a moltencarbonate fuel cell can both provide additional power in the form ofelectrical energy as well as providing an anode exhaust that can beadjusted for use as a syngas input for methanol synthesis. Theelectrical power can typically be used for powering compressors, pumps,and/or other systems at high efficiency. In some aspects, the overallsize of the MCFC system can be set to provide at least a portion of (orpotentially all) necessary on-site power, or optionally additional powercan be generated for the grid. The generation of power on-site can bemore efficient due to reducing or minimizing transmission losses.Additionally or alternately, the electrical power can be readilyprovided as AC, DC, or a mixture of the two, optionally at a pluralityof voltages and currents. This can reduce or potentially eliminate theneed for inverters and/or other power electronics that can further lowerelectrical efficiency. Further additionally or alternately, the MCFCelectrical power can be generated from input fuel materials from whichCO₂ can be captured, as opposed to generation of power from disparateand off-site power sources. This power can be generated in a manner thatcan be integrated into both syngas production and the processing ofvarious purge or off-gas streams.

The output stream from a MCFC anode can contain relatively highconcentrations of H₂, CO₂ and water, with relatively lowerconcentrations of CO. Through a combination of separations, (reverse)water gas shift reactions, and/or other convenient mechanisms, thecomposition of the anode exhaust and/or a stream derived/withdrawn fromthe anode exhaust can be adjusted. The adjustment of the composition caninclude removing excess water and/or CO₂, adjusting the ratio of H₂:CO,adjusting the Module value M, or a combination thereof. For example, atypical MCFC anode output may have an H₂:CO ratio of about 4:1 when theoverall fuel utilization is in the range from about 30% to about 50%. Ifthe anode exhaust is passed through a stage to remove some of the CO₂(for example, a simple cryogenic separation), the CO₂ concentration canbe adjusted downwards until the “M” value is closer to about 2. As abenefit, this type of process can produce a purified CO₂ stream that canbe used for other processes and/or removed to lower the plant's overallCO₂ emissions.

Various configurations and strategies can be used for integrating moltencarbonate fuel cells with methanol synthesis. In one configuration,separations of H₂O and/or CO₂ and/or water-gas shift reactions can beused to adjust the M value of the anode exhaust, and/or a portion of theanode exhaust such as a gas stream can be withdrawn from the anodeexhaust, e.g., to get closer to the desired M value. Additionally oralternately, H₂ production by the fuel cell can be increased/maximized,such as by reducing fuel utilization, e.g., so that an additional H₂stream can also be separated from the anode exhaust and/or from thewithdrawn syngas stream.

In a typical methanol plant, a large percentage of the reactor exhaustcan be recycled after recovery of methanol liquid, due to low conversionper pass. As with most configurations featuring high recycle amounts,buildup of inerts to the process (e.g. methane) can require significantpurge streams that can be rich in non-reactive components. At best,conventional configurations may burn the purge streams for heat tointegration, or more likely the purge streams can just be exhausted tothe environment. It is noted that, in this type of conventionalconfiguration, carbon not incorporated into the methanol can typicallybe exhausted to the environment, potentially resulting in high CO₂emissions.

FIG. 11 schematically shows an example of a configuration that canintegrate an MCFC with a methanol synthesis process. The configurationshown in FIG. 11 can improve on one or more of the deficiencies ofconventional systems. For example, in some configurations, the hotoutput from the MCFC can be fed to a heat recovery steam generationprocess (HRSG) to produce electricity, in addition to the electricaloutput from the MCFC. Additionally or alternately, the process ofadjusting the M value of the syngas can result in a separated productrich in CO₂, which can be used for partial recycle to the fuel cellcathode and/or which can be purified into a separate increased-purityCO₂ product.

In some configurations, the output from the methanol synthesis reactioncan be separated into a liquid alcohol product, a recycle syngas stream,and a vented purge. The vented purge can contain syngas components, fuelcomponents (e.g. methane), and inerts. At least a portion of the ventedpurge can be used as anode and/or cathode feed components. For theliquid alcohol product, typically the collected liquid products can beput into a separation system such as a distillation column, wherepurified methanol can be withdrawn and a bottom product (e.g., comprisedof higher alcohols) can be produced as a waste stream. In a conventionalsystem, the vented purge and/or the waste stream can be used to raisesteam for heating the syngas production. This use in a conventionalsystem can be based in part on concerns about the potential buildup ininerts, if the stream(s) is(are) recycled to the methanol synthesisprocess. By contrast, in various aspects, any byproducts of the methanolsynthesis process (such as the vented purge and/or the heavier alcohols,e.g., containing two or more carbons) can be used in the MCFC system toproduce more syngas and/or as a carbon source (after combustion) toproduce CO₂, e.g., for the cathode. Inerts introduced into the cathodethat are not reformable (e.g. nitrogen) can be exhausted, while excessfuel molecules can converted into heat and into CO₂ that can be readilyused within the cathode. As a result, integration of an MCFC with amethanol synthesis process can allow for improved integration of thesecondary product streams from methanol synthesis, as the MCFC can avoidexcessive buildup of inerts, while still allowing for use of fuelcomponents, as well as allowing for separation of CO₂ into higherconcentration output streams such as the anode exhaust.

Optionally but preferably, the integration of molten carbonate fuelcells with methanol synthesis can include integration with a turbine,such as a gas turbine. Because methanol synthesis can benefit from atleast some CO₂ (as shown in the M value), having an external source ofCO₂ for the cathode inlet of the fuel cell can provide additionalbenefits. Methanol synthesis can require high amounts of electricalpower, at least a portion (or perhaps all) of which can be provided bythe MCFC and/or the gas turbine. If electrical power is provided by theMCFC, at least a portion of the equipment (pumps and compressors) canrun on DC power. Additionally or alternately, if a gas turbine is used,the gas turbine can allow for steam generation, and the steam from theturbine can be used as a driver for the compressors and methanolrecycle. As an example for an integrated system, the input stream forthe anode inlet can be generated by methane reforming (and/or byreforming of another reformable fuel). CO₂ for the cathode inlet cancome from a co-located turbine, from CO₂ separation from the anodeexhaust, and/or from another source. It is noted that providing CO₂ forthe cathode inlet from a source such as a gas turbine, as opposed torecycling CO₂ from the anode exhaust, can avoid the need for apressurize/decompress cycle. Further additionally or alternately, heatintegration can be used so that low level heat from the methanolsynthesis reactor can be used on the front end of the MCFC, e.g., forhumidification.

FIG. 12 schematically shows an example of integration of moltencarbonate fuel cells (such as an array of molten carbonate fuel cells)with a reaction system for performing methanol synthesis. In FIG. 12,molten carbonate fuel cell 1210 schematically represents one or morefuel cells (such as fuel cell stacks or a fuel cell array) along withassociated reforming stages for the fuel cells. The anode output 1215from fuel cell 1210 can then be passed through one or more separationstages 1220, which can include CO₂, H₂O, and/or H₂ separation stages, aswell as water gas shift reaction stages, in any desired order, asdescribed below and as further exemplified in FIGS. 1 and 2. Separationstages can produce one or more streams corresponding to a CO₂ outputstream 1222, H₂O output stream 1224, and/or H₂ output stream 1226. It isnoted that, in some aspects, the CO₂ output stream 1222 and H₂ outputstream 1226 may not be present, due to adjustment of the fuel celloperating parameters to achieve a desired value of M in the syngasoutput. The separation stages can produce a syngas output 1225 suitablefor use as an input for methanol synthesis stage 1230. The methanolsynthesis stage 1230 can produce a methanol product 1235 that can beused directly and/or that can undergo further processing, such as use asa feed in a further process, such as a methanol-to-olefins and/ormethanol-to-gasoline reaction system. Optionally, the CO₂ output 1222from the separation stage(s) 1220 can be used as at least a portion ofthe input (not shown) for the cathode of fuel cell 1210.

As an example of producing and/or withdrawing a syngas stream from theanode exhaust, in an aspect, the effluent or exhaust from an anode canfirst be cooled and then pressurized to MeOH synthesis pressures, suchas a pressure of about 700 psig (about 4.8 MPag) to about 1400 psig(about 9.7 MPag). Separation of the CO₂ in order to achieve a desired Mvalue for the syngas stream, such as by cryogenic separation, can beeasier at such pressures. Additionally or alternately, if the M ratiodeviates from a desired value, the M value can be adjusted, e.g., byrecycle (purge) of the excess syngas through the anode input loop. Insome cases, CO₂ can build up in the recycle loop, and this can berecycled into the (cryogenic) separation loop as well.

FIG. 11 shows another example of an integrated system that includes aMCFC and a methanol synthesis process. In FIG. 11, the configuration canbe suitable for, as an example, conversion of natural gas/methane tomethanol with an integrated MCFC-catalytic reactor system. In this typeof configuration, the MCFC can produce the intermediate syngas that canbe fed to a catalytic reactor for methanol production. In a typicalmethanol form natural gas process, syngas can be generated by methanesteam reforming in an autothermal reactor (ATR). The heat from the ATRcan be recovered to produce electricity and steam for the rest of theprocess. Three commercial processes are documented in SRI ProcessEconomics Program Report 49C on Methanol (See Apanel, George J.,Methanol-Report No. 39C. SRI Consulting, March 2000). A two stageprocess from that report can be used as a representative example of amethanol synthesis process. This two stage process was used as thecomparative basis for the simulations described herein.

FIG. 11 shows a diagram of the integrated process. Vent gases 1101 andheavy (C₂₊) alcohol side products 1102 from the conversion reactors anda fraction of the cathode exhaust 1103 can be returned to the MCFCcathode feed burner 1190. Air 1104, methane 1105, vent gases 1101,alcohol side products 1102, and cathode exhaust 1103 can be combusted toproduce a hot cathode feed 1106. By pre-heating the anode methane feed1107, cathode feed 1106 can be cooled to the inlet operating temperatureand then fed to the cathode. Anode (methane) feed 1107 and steam 1108can be fed to the anode. The MCFC 1130 can produce a hot cathode exhaust1109 depleted of CO₂ and a hot anode exhaust 1110, which can containmostly H₂/CO₂/C0 and water. The MCFC 1130 can be run under a variety ofconditions, including conditions with a reduced fuel utilization, suchas a fuel utilization of about 50% or less. Cathode exhaust 1109 can becooled by partially pre-heating anode methane and/or other fuel feed1107 and then can be sent to a heat recovery steam generation system(HRSG) 1162 to recover more heat and/or to raise steam for the process.The cooled cathode exhaust 1124 can be split into stream 1103, which canbe recycled to the cathode feed burner, and stream 1121 which can beemitted to the atmosphere and/or further treated, if desired (notshown). The remaining heat in 1121 can be recovered in a HRSG 1164. Theanode exhaust 1110 can be sent to a HRSG, such as HRSG 1162. The cooledanode exhaust can be split or divided into streams 1111 and 1112, withstream 1111 being fed to a water-gas shift reactor 1140 to make shifteddivided stream 1113. Shifted divided stream 1113 can be combined withthe second divided stream 1112 and sent to a separator 1150, where itcan be dehydrated 1114 and separated into a syngas stream 1115, withM=approximately 2, and remaining stream 1116, which can contain mostlyCO₂. CO₂-containing stream 1116 can be compressed and sold for useand/or sent to a sequestration facility. The split between streams 1111and 1112 can be determined such that syngas 1115 can have a desired Mvalue for the methanol conversion reactor feed. Syngas 1115 can becombined with a reactor recycle stream 1117. The combined streams can becompressed, heated, and fed to the conversion reactor 1170 to makeeffluent 1118. Effluent 1118 can be, for example, flashed to recover thereactor recycle stream 1117 and a product stream 1119. Methanol 1123 canbe recovered from product stream 1119, while also producing vent gases1101 and heavy alcohol side products (containing 2 or more carbons) 1102as byproducts.

The MCFC process can be sized to produce the necessary syngas feed for amethanol conversion reactor. In the calculations provided in thisexample, the MCFC was sized to produce syngas for a ˜2500 tons per day(tpd) methanol conversion reactor, based on the representative processthat was selected. Based on calculations performed using mass and heatbalance considerations, the MCFC was calculated to produce about 176 MW.Additional details about the process flows are shown in FIG. 13, whichshows the composition of the flows within the FIG. 11 configuration. Thenumbers at the head of each column correspond to the identifiers in FIG.11. Part of the power generated by the MCFC can be used for syngasseparation and compression, while the remainder can be used in otherparts of the process and/or exported. Additionally, based on thecalculations, the heat recovered from the MCFC anode and cathodeeffluent streams generated at least ˜3146 tpd of high pressure steam,which was enough to meet steam and heating demands of the representativemethanol synthesis process modeled in the calculations. It is notedthat, for the calculation involving the MCFC, any utilities associatedwith autothermal reforming were not considered in determining if theMCFC could provide the inputs for the synthesis process. Under theassumption that separated CO₂-containing stream 1116 can be sold for useand/or sequestered, the integrated process shown in FIG. 11 can providea method to produce methanol from natural gas (methane) with reduced CO₂emissions, compared to a traditional process. Table B shows the amountof CO₂ that was calculated as being emitted from the selected literaturecomparative configuration, along with the reduced CO₂ emissions thatwere calculated based on the configuration in FIG. 11. For the base casecalculation in Table A, it was assumed that the vent from theautothermal reformer and the exhaust from the natural gas boiler werethe largest emission sources.

TABLE B kg CO₂/kg MeOH produced 2 stage process (base case) 0.318 MCFC +2 stage process conversion reactor 0.025

It is noted that some dimethyl ether (DME) and butanol (C₄H₉OH) can begenerated during the methanol synthesis process. Dimethyl ether can bean example of a subsequent product that can be produced using methanolgenerated in a methanol synthesis process. More generally, methanol canbe used to generate a variety of additional products, such as dimethylether, olefins, fuels such as naphtha and/or diesel, aromatics, andother industrially useful products, as well as combinations thereof. AnMCFC can additionally or alternately be integrated into synthesisprocess where the output from a methanol synthesis plant is passed intoan additional reaction system for production of another product. Suchintegration can include providing syngas inputs, providing electricityfor the system, handling output streams of lower value, and/orseparating out streams having increased concentration of CO₂, asdescribed above for integration with a methanol synthesis process.

Integration with Production of Nitrogen-Containing Intermediate andFinal Products

Ammonia can typically be made from H₂ and N₂ via the Haber-Bosch processat elevated temperature and pressure. Conventionally, the inputs can bea) purified H₂, which can be made from a multi-step process that cantypically require steam methane reforming, water gas shift, waterremoval, and trace carbon oxide conversion to methane via methanation;and b) purified N₂, which can typically be derived from air via pressureswing adsorption. The process can be complex and energy intensive, andthe process equipment can benefit strongly from economies of scale. Anammonia synthesis process utilizing molten carbonate fuel cells canprovide one or more advantages relative to a conventional process,including but not limited to additional power production, reducedcomplexity, and/or better scalability. Additionally or alternately, anammonia synthesis process utilizing molten carbonate fuel cells canprovide a mechanism to reduce CO₂ production and/or generate CO₂ for usein other processes.

In various aspects, the MCFC system can generate syngas as an output.The syngas can be largely free of any impurities such as sulfur thatwould need removal, and the syngas can provide a source of H₂ for theammonia synthesis. The anode exhaust can first be reacted in a water-gasshift reactor to maximize the amount of H₂ relative to CO. Water-gasshift is a well-known reaction, and typically can be done at “high”temperatures (from about 300° C. to about 500° C.) and “low”temperatures (from about 100° C. to about 300° C.) with the highertemperature catalyst giving faster reaction rates, but with higher exitCO content, followed by the low temperature reactor to further shift thesyngas to higher H₂ concentrations. Following this, the gas can undergoseparation via one or more processes to purify the H₂. This can involve,for example, condensation of the water, removal of CO₂, purification ofthe H₂ and then a final methanation step at elevated pressure (typicallyabout 15 barg to about 30 barg, or about 1.5 MPag to about 3 MPag) toensure that as many carbon oxides as possible can be eliminated. Inconventional ammonia processes, the water, CO₂, and methane streamsgenerated during purification of the H₂ stream, as well as additionaloff-gases from the ammonia synthesis process, can represent wastestreams of very low value. By contrast, in some aspects, the various“waste” gases can create streams that can be used in other parts of theMCFC—Ammonia system, while potentially generating still other streamsthat can be useful in further processes. Lastly, the H₂ stream can becompressed to ammonia synthesis conditions of about 60 barg (about 6MPag) to about 180 barg (about 18 MPag). Typical ammonia processes canbe performed at about 350° C. to about 500° C., such as at about 450° C.or less, and can result in low conversion per pass (typically less thanabout 20%) and a large recycle stream.

As an example of integration of molten carbonate fuel cells with ammoniasynthesis, the fuel stream to the anode inlet can correspond to freshsources of reformable fuel and/or H₂ along with (optionally butpreferably) recycle off-gas from the ammonia synthesis process, whichcan contain H₂, CH₄ (or other reformable hydrocarbons), and/or CO.Ammonia processing, due to large recycle ratios and the presence ofdiluents (for example: the methane produced by methanation to remove allcarbon oxides), can produce significant purge and waste streams. Most ofthese streams, as long as they do not contain reactive oxidants such asoxygen, can be compatible with the fuel cell anode inlet. The anodeinlet can additionally or alternately comprise separation gases fromhydrogen purification, as these gases can typically contain a mixturethat comprises H₂, CO, CO₂, H₂O, and potentially other gases compatiblewith the anode. The anode exhaust can then be processed using a watergas shift reaction and H₂ separation to form a high purity H₂ stream. Atleast a portion of such an H₂ stream can then be used as an input for anammonia synthesis process. Optionally, in addition to performingseparations on the high purity H₂ stream, the H₂ stream can be passedthrough a methanator prior to use for ammonia synthesis. The goal of theone or more separations and/or purifications can be to increase thepurity of the H₂ stream, so that at least a portion of an H₂ stream withincreased purity can be used as an input for the ammonia synthesis.

For the cathode inlet stream, CO₂ and O₂ can be provided from anyconvenient source, such as a co-located external CO₂ source (forexample, a gas-turbine and/or boiler exhaust stream), recycled CO₂separated from the anode exhaust, recycled CO₂ and/or O₂ from thecathode exhaust, carbon containing streams separated as part of hydrogenpurification, and/or CO₂ separated from an output of the ammoniasynthesis plant. Typically, a mixture of these streams may be usedadvantageously, and any residual fuel value in the streams can be used,e.g., to provide heat to raise the cathode inlet stream temperature upto the MCFC inlet temperature. For example, fuel streams that areoff-gasses from separation and/or the ammonia process can be mixed withsufficient oxidant (air) to combust substantially all the residual fuelcomponents while also providing sufficient oxygen to react with CO₂ inthe cathode to form carbonate ions. The cathode exhaust stream can havereduced concentrations of both CO₂ and O₂, as these gases can be reactedto form carbonate that can be transported into the anode stream. Becausethe MCFC can reduce the CO₂ and O₂ content of the cathode inlet stream,the cathode exhaust can have an enhanced nitrogen concentration on a drybasis in comparison to air. For systems that are designed to separateCO₂ effectively, the cathode exhaust may have CO₂ concentrations belowabout 10% or below about 5% or below about 1% on a dry basis. The oxygencontent may additionally or alternately be below about 15% or belowabout 10% or below about 5% on a dry basis. The N₂ concentration cantypically exceed about 80% or about 85% or can be greater than about 90%on a dry basis. After capture of the heating value of this stream (suchas through steam generation for heat, heat exchange with other processstreams, and/or additional electricity), the cathode exhaust canoptionally but advantageously be used to form a high purity N₂ streamfor use in the ammonia synthesis. Any of the typical separation methodsfor generating pure nitrogen can operate more efficiently on thisstream. Optionally, one or more separation processes or purificationprocesses can be performed on the N₂ stream in order to generate an N₂stream of increased purity. At least a portion of the N₂ havingincreased purity can then optionally but advantageously be used as theinput for ammonia synthesis. During operation, the fuel cell can beoperated to match the needs of the ammonia synthesis, such as selectedlower or greater amounts of electrical production relative to hydrogen(and/or syngas) production.

Relative to conventional systems (such as described in U.S. Pat. No.5,169,717), the above integration method can reduce or eliminate theneed for a separate front end system for generating the purified H₂ andN₂ input streams. For example, instead of having a dedicated steamreformer and subsequent cleanup stages, the MCFC can be operated toreform sufficient amounts of reformable fuel to provide purified H₂while also generating electrical power. Typically this can be done byoperating the fuel cell at lower fuel utilizations than typical. Forexample, the fuel utilization can be below about 70%, such as belowabout 60% or below about 50% or below about 40%. In conventional MCFCoperations, fuel utilizations of about 70-80% can be typical, and theresidual syngas produced by the anode can be used as fuel to heatincoming streams to the cathode and/or anode. In conventionaloperations, it can also be necessary to use the anode exhaust stream toprovide CO₂ to the cathode after it is reacted with air. By contrast, insome aspects it is not necessary to use syngas from the anode exhaustfor simple combustion and recycle. The ammonia synthesis process canprovide a number of waste or purge streams which may be utilized,maximizing the amount of syngas available for ammonia synthesis.Similarly, as noted above, the cathode exhaust from the MCFC can providea higher purity initial stream for forming the purified N₂ stream.Concentrating the generation of input streams for ammonia synthesis inthe MCFC and associated separation stages can reduce the equipmentfootprint as well as providing improved heat integration for the variousprocesses.

Urea is another large chemical product that can be made by the reactionof ammonia with CO₂. The basic process, developed in 1922, is alsocalled the Bosch-Meiser urea process after its discoverers. The variousurea processes can be characterized by the conditions under which ureaformation takes place and the way in which unconverted reactants arefurther processed. The process can consist of two main equilibriumreactions, with incomplete conversion of the reactants. The net heatbalance for the reactions can be exothermic. The first equilibriumreaction can be an exothermic reaction of liquid ammonia with dry ice(solid CO₂) to form ammonium carbamate (H₂N—COONH₄):2NH₃+CO₂

H₂N—COONH₄

The second equilibrium reaction can be an endothermic decomposition ofammonium carbamate into urea and water:H₂N—COONH₄

(NH₂)₂CO+H₂O

The urea process can use liquefied ammonia and CO₂ at high pressure asprocess inputs. In prior art processes, carbon dioxide is typicallyprovided from an external resource where it must be compressed to highpressure. In contrast, the current process, as shown in FIG. 6, canproduce a high pressure liquefied carbon dioxide stream suitable forreaction with the liquid ammonia product from the ammonia synthesisreaction.

In various aspects, urea production can be improved by providing one ormore inputs (e.g., electric, heat, CO₂, NH₃, H₂O) and/or accepting oneor more outputs (e.g., H₂O, heat) from the MCFC while eliminating theneed for a large number of separate systems. Additionally, as with mostequilibrium processes involving substantial product removal and recycle,purge or waste streams can be generated. These purge or waste streamscan be the result of side reactions and impurity buildup within therecycle loop. In a typical stand-alone plant, these streams can often beof low value, and potentially can require further purification, withadditional processes and equipment, for recycle. By contrast, in variousaspects, the purge or waste streams can be used advantageously and in amuch simpler fashion. The anode inlet can consume any reformable fueland/or syngas composition. Streams diluted with materials that can becombusted, for example, nitrogen compounds such as ammonia, can bereacted with air to produce N₂, water and heat which can be utilized aspart of the cathode inlet along with any streams containing residualCO₂, CO, and H₂. As the MCFC system can typically be operated at lowpressure (below about 10 barg or about 1 MPag and often near-atmosphericconditions), there can be a reduced or minimized need to recompress anyof the purge or waste streams, as these process streams can besufficiently pressurized for MCFC use.

Additionally, the urea process can be integrated into a combined systemwith an ammonia synthesis process. This integrated approach can reduceand/or eliminate many processes from the conventional approach, whichcan require an ammonia plant (steam reformer, water gas shift, pressureswing adsorption to produce H₂+air separation plant) plus a separatesupply of cold CO₂ (dry ice) typically made remotely and thentransported to the plant. The current system can eliminate many of theseprocesses and, as it can separate a CO₂ stream at high pressure, canprovide the necessary reactants at advantageous conditions.Specifically, rather than transport CO₂ as dry ice for use at a remoteurea plant, carbon dioxide can be provided from separation of a streamderived from the MCFC anode exhaust in liquefied form, and thus caneasily be compressed to appropriate reaction pressures. This can avoidsubstantial energy inefficiencies in cooling, transport andrecompression of the CO₂.

As described above, an MCFC can be integrated with an ammonia plant forammonia production while reducing or minimizing the amount of additionalequipment. Additionally or alternately, a separation can be performed onthe anode exhaust from an MCFC system to provide a source of CO₂. Thissource of CO₂ can then be further separated and/or purified so that atleast a portion of the CO₂ can be used for the urea synthesis process.For example, CO₂ separation can be performed using a process comprisingcryogenic separation. This can reduce or eliminate the need for separateproduction and/or transport of cold CO₂. Further additionally oralternately, the MCFC system can provide electric power and/or canprovide or consume heat by heat exchange with the MCFC inputs/outputstreams and/or by heat exchange with the separation systems.

FIG. 16 schematically shows an example of integration of moltencarbonate fuel cells (such as an array of molten carbonate fuel cells)with a reaction system for performing ammonia synthesis and/or ureasynthesis. In FIG. 16, molten carbonate fuel cell 1610 can schematicallyrepresent one or more fuel cells (such as fuel cell stacks or a fuelcell array) along with associated reforming stages for the fuel cells.

The fuel cell 1610 can receive an anode input stream 1605, such as areformable fuel stream, and a CO₂-containing cathode input stream 1609.In FIG. 16, anode input stream 1605 can include an optional recycledportion of an off-gas 1647 produced by the ammonia synthesis process1640. In FIG. 16, cathode input stream 1609 can include an optionalrecycled portion of CO₂ 1629 separated from the anode and/or cathodeoutput of the fuel cell 1610 in separation stages 1620. The anode output1615 from fuel cell 1610 can then be passed through one or moreseparation stages 1620, which can include CO₂, H₂O, and/or H₂ separationstages, optionally as well as water gas shift reaction stages, in anydesired order, as described below and as further exemplified in FIGS. 1and 2. Separation stages can produce one or more streams correspondingto a CO₂ output stream 1622, H₂O output stream 1624, and a high purityH₂ output stream 1626. The separation stages can also produce anoptional syngas output 1625. A cathode output 816 can be passed into oneor more separation stages 1620. Typically, the separation stage(s) usedfor the cathode output can be different from the separation stage(s) forthe anode output, but the resulting streams from the separation canoptionally be combined, as shown in FIG. 16. For example, CO₂ can beseparated from the cathode output 1616 and added to one or more CO₂output streams 1622. The largest product separated from the cathodeoutput 1616 can be a high purity N₂ stream 1641. The high purity H₂output stream 626 and the high purity N₂ stream 1641 can be used asreactants for ammonia synthesis stage 1640 to generate an ammonia outputstream 1645. Optionally, a portion of the ammonia output stream can beused as an input 1651 for urea production 1650, along with CO₂ stream(s)622 from the separation stages 620, to generate a urea output 1655.Optionally, the input ammonia stream 1651 for urea production 1650 canbe from a different source. Optionally, either the ammonia productionstage 1640 or the urea production stage 1650 can be omitted from theconfiguration.

Integration with Production of Biofuels and Chemicals by Fermentation

Biofuels or biochemical can frequently be produced by a process offermentation of carbohydrates derived from crops such as corn, sugar, orlignocellulosic materials like energy grasses. The most common exampleof this process includes ethanol manufacture, such as from corn. Thisprocess can typically require inputs of heat (for distillation),electricity (for general plant operations), and water (for processingraw materials, cleaning and other processes), and can produce—inaddition to standard products—CO₂. CO₂ can be produced via thefermentation reaction in which sugar (C₆H₁₂O₆) can be converted to 2C₂H₅OH (ethanol)+2 CO₂. Fermentations to other products, such asbutanol, higher alcohols, other oxygenates and the like, can producesimilar products and can require similar inputs. The greenhouse gasemissions and overall economics of the plant can all be influenced bythe efficiency in producing and/or providing these inputs and outputs.Other sources of carbohydrates or sugars can go through similarprocesses to yield desired bio-products and can result in someconversion of the original carbohydrates to sugar.

In various aspects, the combination of an MCFC system, such as an MCFCsystem using natural gas as a reformable fuel, with ethanol manufacturecan provide a variety of advantages. This can be due in part to the factthat the MCFC system can provide essentially all the needed inputs whilealso consuming the CO₂ output from the ethanol plant. This can lower thegreenhouse gas emissions, reduce water requirements, and/or increaseoverall efficiency.

The ethanol plant can use the electricity from the MCFC to poweroperations and the residual heat from the MCFC to provide heat toprocesses like distillation. The exact requirements of the plant (mix ofheat to electric) can be managed by adjusting the overall fuelutilization of the MCFC plant, such as by producing extrahydrogen/syngas as the medium to provide more or less heat relative toelectrical output. Alternately or in addition, the fuel sources to theMCFC can be adjusted to balance inputs and outputs for a given plantconfiguration and a given set of inputs, such as by using some of thefermentation product as anode feed, and/or by using heat and/or productsfrom associated inputs, like non-fermentable biomass, as inputs. Theelectrochemical process can typically produce water by virtue of thereaction of carbonate ions with hydrogen; said water can be condensedfrom the anode outlet. Additional water may be produced in theproduction of excess syngas, e.g., via the water-gas shift reaction. Thewater can then be used as process water in the plant, as it can tend tobe very pure and rather free from impurities. Example water uses includebut are not limited to the dry milling process, where water can be addedto corn that has been ground, and/or the wet milling process, where corncan be soaked in a solution of acid and water. The fermentation CO₂output can be used as cathode input and, if needed, can be supplementedby recycle of anode outlet CO₂ and/or via burning of fresh fuel (methaneand/or natural gas) to raise additional heat. As all the heat processesin an ethanol plant can typically be at relatively low temperature(e.g., distillation<100° C.), nearly all the waste heat of the MCFCsystem can be efficiently consumed.

A set of different configurations may be used for the MCFC inputs andoutputs depending on specific plant configurations and feed stocks. Forsome configurations, the process can use the ethanol product, mixed withwater, as the anode input fuel and can thus avoid, or reduce, the amountof natural gas required. Ethanol, made in fermentation, can be partiallydistilled, separated, or extracted, for instance to a molar ratiobetween about 1H₂O:1 EtOH and about 4:1, such as from about 1.5:1 toabout 3:1, or of about 2:1. This mixture can then be reformed with heatin and/or outside of the fuel cell to produce a mixture comprisinghydrogen gas that can then be input to the anode. While the overallplant output of ethanol can be reduced, the amount of non-biologicallybased inputs can be reduced or eliminated from the process, resulting inlower life-cycle CO₂ emissions.

For some configurations, burning lignin sources such as corn stover,wood, and/or sugar bagasse could supplement and/or replace the input oftraditional hydrocarbon fuels like methane. This can allow the plant tobe self-sufficient in energy and can reduce the need to integrate intosupply chains that could incur life cycle emissions debits. For theseconfigurations, the lignin sources can produce heat, and, if partiallyoxidized to a gaseous mixture comprising syngas, the syngas can be usedas input to the MCFC system. Lignin sources can be burned and used toprovide some electricity (via steam production and steam turbine), whilethe exhaust gas from the process can provide the CO₂ input to the MCFCsystem.

For some configurations, the input CO₂ for the cathode inlet can bederived from separation of CO₂ from the anode output syngas mixture.This separation may occur before or after the stream can be used toproduce heat for various processes (including additional powergeneration through steam production), and/or before or after the streamcan be used to provide hydrogen to a process and/or to provide heat.Typically, this type of approach can be used where it may be desirableto capture the CO₂. For example, the anode outlet can be passed to a CO₂separations stage where most of the CO₂ can be captured and where theresidual syngas can then be used for heat, electrical, and/or chemicalprocesses. The output from these processes can then be returned to thecathode along with potentially added methane and/or oxidant (air), toprovide a cathode inlet with the proper temperature and gas composition.

Alternatively, for some configurations where CO₂ capture may not bedesired, the CO₂ output from the fermentation system can be used as atleast part of the (if not the entire) CO₂ source for the cathode whenmixed with oxidant (air) and raised to the proper inlet temperature. Forthese configurations, the anode output may be used for heat, electrical,and/or chemical purposes, and the resulting final stream containingcombusted syngas may be vented and/or partially returned as feed to thecathode inlet. Any one or a combination of these configurations may bedesirable, depending on the plant configuration and requirements for CO₂emissions. For example, some CO₂ from fermentation can be combined withresidual syngas streams after use for various heat, electrical, and/orchemical processes, and the combined stream can be reacted with oxidant(air) to provide oxygen to the cathode and raise the temperature of thecathode inlet stream.

The anode outlet stream from the MCFC can be used for a variety ofdifferent processes. In one configuration, this stream can be used toprovide heat for distillation and may involve combustion of the residualsyngas in the anode outlet to raise additional heat for the distillationprocess. For this configuration, oxidant (air) can be added to theoutlet stream, and the stream sensible heat and heat of combustion cantypically be used to raise steam that can then be used to provide theenergy for distillation. Optionally, the exhaust from this process, withor without the addition of the fermentation process, can be used as thecathode inlet before and/or after optional separation of some of theCO₂.

For some configurations, the anode outlet gas can be used as a source ofhydrogen without further processing, after a shift reaction, and/orafter separation of some CO₂ as a source of hydrogen. The hydrogen canbe used for a variety of processes. These processes may include but arenot limited to production of additional, largely carbon-free,electricity by combustion in a hydrogen turbine. Additionally oralternatively the hydrogen can be used for a chemical process such astreating other biofuel products. For example, lignocellulosic materialsunsuited to fermentation (e.g. corn stover and/or sugar bagasse) canundergo a thermochemical process such a pyrolysis to produce anunstable, high oxygen product unsuited for use in fuels. A variety ofprocesses may be used such as pyrolysis, fast pyrolysis, and/orhydropyrolysis, any/all of which may be accomplished with or withoutcatalysts. Typically these products can contain residual oxygen that canreduce the products heating value and can often greatly reduce theirstability in storage, transportation, and use. These types of productscan advantageously be treated with hydrogen to produce a fuel compatibleblend stock (pyrolysis oil) that can optionally be blended with thefermentation product to increase the overall production of biofuels.

Another use for hydrogen can be in the co-production of biodieselmaterials. Typically, starch sources (for example, corn, sugar) can beused to make ethanol for use in gasoline fuels, while other crops heavyin “oils” (e.g., tri-acyl glycerides) such as soybeans or palms can beused to produce longer-chained molecules that may be suitable for dieselfuel and/or jet fuels, as is and/or after upgrading. Other renewableresources can contain even longer-chained molecules that may suitablefor lubricants and/or heavier fuels such as bunker/marine fuels and/orhome heating oils, as is and/or after upgrading. These materials cantypically require some processing involving hydrogen, especially whenthe desired product can be largely oxygen free e.g., in the case of ahydro-treated vegetable oil instead of a fatty acid methyl ester (FAME)product). As biofuel products and crops may be largely co-located, theavailability of hydrogen may aid in a variety of processing schemes.

In some aspects, a goal of the integrated MCFC and fermentation systemcan be to reduce or minimize the overall CO₂ production from thefermentation plant. In an example of such a system, biomass feed canenter a fermentation plant and undergo optional processes to prepare thematerial for fermentation (for example, grinding, water treatment). Theelectrical energy and water for the process can be at least partially(if not totally) provided for by the fuel cell outputs. The fermentationprocess can produce a biofuel plus secondary products (for example,distiller's dry grains), and a gas stream comprising a relatively highamount of CO₂. A biofuel product from the fermentation plant mixed withan appropriate amount of water can be used as an anode input fuel to theMCFC. Depending on the aspect, the biofuel product can correspond to atleast a portion of the fermentation product, at least a portion of abiogas or other fuel derived from a residual or secondary product of thefermentation, or a combination thereof. Syngas from the MCFC anodeoutlet can be combusted to provide at least some (if not all required)heat for all plant processes including distillation. The anode outletproduct can be used before and/or after a CO₂ separation process.Alternatively, the anode outlet can be split, so that some of the anodeoutlet stream can be used to provide at least some heat for thefermentation plant processes, while a second stream can be used toprovide heat for a different purpose, such as to preheat the cathodeinput stream. Some of the resulting CO₂ containing streams can becombined with air and used as a cathode inlet stream. The overallprocess can advantageously use no external energy source and couldtypically emit CO₂ only derived from biological processes.Alternatively, a CO₂ separation scheme can be added at any one or moreof various points, such as after the anode and/or after all the CO₂streams are combined. This stage can provide a substantially pure CO₂output stream for sequestration and/or for some other use. In thisconfiguration, the overall plant CO₂ emissions, from a life-cycle basis,can be negative (less than zero net CO₂ produced), as biologicallyderived CO₂ can be removed for sequestration with proportionally fewer(without any) external carbon-based fuel inputs.

FIG. 15 schematically shows an example of integration of moltencarbonate fuel cells (such as an array of molten carbonate fuel cells)with a reaction system for performing alcohol synthesis, such as ethanolsynthesis. In FIG. 15, molten carbonate fuel cell 1510 schematicallyrepresents one or more fuel cells (such as fuel cell stacks or a fuelcell array) along with associated reforming stages for the fuel cells.The fuel cell 1510 can receive an anode input stream 1505, such as areformable fuel stream, and a CO₂-containing cathode input stream 1509.Optionally, the anode input stream can include fuel from an additionalsource 1545, such as methane derived from lignin and/or corn stover bycombustion and subsequent methanation. Optionally, the cathode inputstream 1509 can include an additional CO₂-containing stream 1539 derivedfrom the CO₂ generated during fermentation to make ethanol (or anotherfermentation product). The cathode output from fuel cell 1510 is notshown in FIG. 15. The anode output 1515 from fuel cell 1510 can then bepassed through one or more separation stages 1520, which can include oneor more of CO₂, H₂O, and/or H₂ separation stages, and/or one or morewater gas shift reaction stages, in any desired order, e.g., asdescribed below and as further exemplified in FIGS. 1 and 2. Separationstages can produce one or more streams corresponding to a CO₂ outputstream 1522, H₂O output stream 1524, and/or H₂ (and/or syngas) outputstream 1526. The H₂ and/or syngas output stream (collectively 1526),when present, can be used, for example, to provide fuel for distillationof ethanol by ethanol processing plant 1560. H₂O output stream 1524,when present, can provide water for the ethanol processing plant 1560.Additionally or alternately, the MCFC 1510 can generate electrical power1502 used by ethanol processing plant 1560. Ethanol processing plant1560 can generate an ethanol (and/or other alcohol) output 1565 that canpreferably be at least partially distilled to enhance the alcoholconcentration of the product. It is noted that the configuration in FIG.15, or any of the other configurations described above, can be combinedwith any of the other alternate configurations such as the use of ligninsources or the co-production of other biofuels.

Example of Integrated MCFC and Fermentation System

This example demonstrates an integrated MCFC and cellulosic ethanolfermentation process to produce ethanol, hydrogen, and electricity withlow CO₂ emissions. One focus of this example can be on the integrationaspects with an MCFC system. The fermentation processes, such as forethanol fermentation, can correspond to a conventional fermentationmethod. For purposes of providing an example, to the degree that detailsof an ethanol fermentation method were needed, a literature referencewas used to provide a representative fermentation process. (See Humbird,et al, Process Design and Economics for Biochemical Conversion ofLignocellulosic Biomass to Ethanol, NREL. May 2011.) The base ethanolfermentation process described in this reference corresponds to a ˜520ton/day fermentation plant. However, any other convenient fermentationprocess could have been substituted into this example. In this example,ethanol can produced from fermentation of stover feedstock. The rejectedbiogas and biomass from the fermentation process can be burned toproduce steam and power for the process, with some excess power beingsold back to the grid. In this integrated MCFC-fermentation process, theMCFC can use a methane-steam mixture as the anode feed and mixture ofCO₂ gases from the fermentation system as the cathode feed. The hot MCFCanode exhaust can be integrated with the steam system to produce enoughlow pressure steam to provide the distillation column heating demand. Itis noted that this can also increase the steam rate through an existingsteam turbine/HRSG system. The anode exhaust can be shifted andseparated into H₂ and CO₂ product streams. The MCFC can produce at leastenough power for the anode exhaust gas separation and compression of thegases to pipeline conditions.

FIG. 14 shows an example of the MCFC portion of the configuration. InFIG. 14, steam 1401 and pre-heated methane 1402 can be fed to the anodeof the MCFC 1450. The MCFC 1450 can produce a mixture 1403 of mostlyH₂/CO/CO₂ at high temperature. Depending on the aspect, the MCFC can beoperated at a low fuel utilization of about 25% to about 60%, such as afuel utilization of at least about 30%, or at least about 40%, or about50% or less, or about 40% or less. Additionally or alternately, the MCFCcan be operated at a more conventional fuel utilization of about 70% orgreater, but this can be less preferable, as the amount of potential H₂that can be recovered from the anode exhaust would be reduced at higherfuel utilizations. Heat can be recovered from mixture 1403, for example,in heat exchanger 1460 to make low pressure steam 1408 from an inputwater stream 1407. Input water stream 1407 can be derived from anyconvenient source, such as water recovered from cathode outlet stream1414 and/or anode outlet stream 1403. Low pressure steam can be used,for example, to provide heat for distillation, such as heat for beercolumn 1442 shown in FIG. 14. Cooled anode exhaust 1404 can be shiftedto produce a mixture of mostly H₂/CO₂ in a water-gas shift reactor 1470.These gases can be separated in one or more separation stages 1480 intoH₂ stream 1405 and CO₂ stream 1406. H₂ stream 1405 and CO₂ stream 1406can be compressed and sold for use. Additionally or alternately, atleast a portion of CO₂ stream can be directed to sequestration. In analternate but less preferable configuration where low CO₂ emissions arenot necessary, CO₂ stream 1406 could be emitted to the atmosphere. Thecathode feed 1409 can be comprised of a mixture of off gas streams ofthe fermentation process. In the example shown in FIG. 14, cathode feed1409 can made up of the vent scrubber off gas 1431 and biogas combustoroff gas 1433, which can account for ˜94% of the CO₂ emitted from thefermentation process. Additionally or alternately, cathode feed 1409 caninclude cellulose seed fermenter off gas 1435, cellulose fermenter offgas 1437, aerobic digester off gas 1439, and/or any other fermenterand/or digester off gases. The off gas (or off gasses) may pass througha gas cleanup system 1448 to pre-treat the cathode feed. The off gasmixture 1409 can be combined with fuel (CH₄) 1410 and oxidant (air) 1411in a burner 1490 and combusted to heat the cathode feed to MCFCoperating temperature. The additional heat in burner output 1412 can beused to pre-heat the methane anode feed 1402. The cathode exhaust 1414can be sent to a HRSG to recover any heat and then emitted to theatmosphere and/or can be sent for further processing, if desired.

Table 2 shows an example of the amount of reduction in CO₂ emissions fora configuration similar to FIG. 14 in comparison with performing thesame conventional fermentation process without using an integrated MCFCsystem. For the calculation shown in Table 2, it was assumed that allcarbon used in the system corresponded to carbon originally derived froma biogenic source. As shown in Table 2, integration of a fermentationprocess with an MCFC system can have the potential to substantiallyreduce CO₂ emissions from ethanol fermentation. Instead of allowing theCO₂ generated by the fermentation process to escape to the atmosphere,using at least a portion of that CO₂ to form some or all of the cathodeinlet stream can allow the majority of that CO₂ to be separated into therelatively pure anode outlet stream. The CO₂ can then be separated outfrom the anode outlet stream in an efficient manner (such as separatingout at least about 90% of the CO₂, such as at least about 95%),resulting in sequestration of the CO₂. In particular, if the originalsource of carbon is considered, where carbon originally derived from abiogenic source may not count against the carbon input to the system,the net CO₂ emissions from the integrated system can actually benegative. This can reflect the fact that carbon originally consumed fromthe atmosphere by plant life (biogenic carbon) has been captured as CO₂and sequestered in such a process, resulting in a net removal of carbonfrom the environment.

TABLE 2 Reduction in CO₂ emissions due to MCFC integration EtOH H₂ CO₂CO₂ Emissions Production Production Emissions corrected for [ton/ [ton/[kg CO₂/ biogenic sources day] day] GJ] [kg CO₂/GJ] Base case 520 0 1720 Integrated Case 520 265 25 −147Integration with Algae Growth and Processing

Algae farms (photosynthetic algae) that have been proposed for use inmaking biodiesel require several inputs: water, CO₂, sunlight,nutrients, primarily nitrogen, possibly heat. In an aspect, moltencarbonate fuel cells can be integrated with the needs of an algae farm(and potentially other processes) to provide a more efficient overallprocess with reduced costs and reduced CO₂ emissions.

In an aspect, CO₂ produced by an MCFC can be used as a CO₂ source forthe algae farm. Additionally or alternately, the inputs and outputs froman MCFC can be integrated with algae farms to do one or more of thefollowing: 1) to use the water produced from the MCFC anode exhaust asmake-up water for the algae; 2) to use the heat produced to heat theponds during evenings/low temperature seasons; 3) to use the electricityproduced by the MCFC to run circulation devices and other processes; 4)to use biomass offgas (e.g. an anaerobic digester) as the source offuel/methane for the MCFC; 5) to use a different biomass aftergasification (algae biomass, lignin) as the source of H₂/CO for theanode; 6) to use a CO₂ producing bioprocess (e.g. fermentation) as theCO₂ source for the cathode, to capture that CO₂ via separation in theanode and then to transfer that CO₂ to the algae after separation (e.g.,to take CO produced from corn to ethanol, and to use it for algae growthto make other products); and 7) to use H₂ and/or N₂ produced by the MCFCto make nitrogen-containing compounds (e.g. NH₃, urea) for use as corenutrient to the algae production.

One benefit of the aspects described above can be that the MCFC processand subsequent separations can make very “clean” CO₂ substantially freeof contaminants typical of exhaust streams such as power plant effluentsor other CO₂ sources. The Integration benefits shown above canadditionally or alternately allow for—depending on configuration—a largenumber of integrated pieces to fit together. For example, use of an MCFCcan create a synergism between CO₂ producing processes and CO₂ consumingprocesses. In such synergistic processes, the MCFC can act as anintermediary that concentrates, separates, and uses the CO₂ in anefficient manner. The MCFC can further additionally or alternately beconfigured with a typical external CO₂ source (e.g. power plant,turbine), so that the MCFC can be used to a) concentrate, b) purify, andc) deliver the CO₂ to the algae growth environment in an easy to useform. This can be a notable improvement over just passing dilute CO₂with contaminants to the algae.

Integration with Cement Manufacture

Concrete and steel are important infrastructure building materials thatcan account for the majority of mass, cost and carbon dioxide emissionsin the building of major infrastructure projects. For example, concreteis currently responsible for about 5% of CO₂ emissions worldwide. Of thetotal emissions, the manufacture of cement, for example Portland cement,represents about 95% of the total emissions from the final product. TheCO₂ can be primarily generated from two sources: the decomposition ofcalcium carbonate to calcium oxide and CO₂, and the heating of cementkilns to temperatures as high about 1800° C., which is typically donewith coal as a fuel. Cement is made in hundreds of plants (about 150-200in the US), typically near quarries where the constituent rock is found.

Manufacture of cement typically involves heating a mixture of materialsto very high temperatures. The major constituents can include limestone(CaCO₃) along with one or more of silica (sand), iron ores, alumina(shale, bauxite, other ores), and/or other materials. The constituentscan be crushed and mixed, after which they can be introduced into a kilnat very high temperatures, typically in air, and typically attemperatures of at least about 1400° C., such as at least about 1800°C., and sometime up to about 2000° C. or greater. Under these conditionsa product, referred to as clinker, can be produced. Clinker can be astable product typically ground in order to form a commercial cement. Inthis discussion, a clinker can be referred to as a cement product. Theprocess to form the cement product can typically result in onesignificant chemical change: the decompositions of limestone to CaO andCO₂. The other ores, starting as oxides, typically do not changechemically. After some cooling, the cement product can typically bemixed with other components, such as gypsum, and optionally ground toachieve the final desired characteristics suitable for use in cementapplications and/or concrete production.

In general, the MCFC can be used as a resource for management of CO₂ byusing CO₂ from the cement manufacture process as an input for thecathode. The amount of CO₂ released by traditional cement manufacturecan typically be at least about 50% from the decomposition of the CaCO₃and about 50% or less due to heating based on combustion ofcarbon-containing fuels, with the amounts potentially varying dependingon the characteristics of an individual manufacturing operation.Additionally or alternately, concrete and cement manufacture can requireelectricity and mechanical energy for the overall process. Whentypically co-located, or closely located with local resources, such asquarries for production of minerals, transport, grinding, a variety ofmechanical processes associated with the cement production process canconsume a large amount of electricity. These energy needs can be met atleast in part by electricity generated by an MCFC integrated with thecement plant. Further additionally or alternately, separation stepsperformed on the anode exhaust can produce water, and this water can beused to mitigate and/or satisfy the water needs of the typical cementplant. Optionally, the MCFC can be operated at low fuel utilization toprovide hydrogen as a fuel, which can still further additionally oralternately remove or mitigate CO₂ emissions due to fuel combustion.

In an aspect, an MCFC system can be integrated with a cement productionplant to use cement effluent as a CO₂ source while also using the MCFCheat and electricity to power the production plant. This firstconfiguration can consume the main source of CO₂ and can also mitigatesome of the secondary sources of CO₂ due to heat and electrical demand.The net result can be a lower carbon emissions cement manufactureprocess with the possibility of carbon capture.

In an additional or alternate configuration, an MCFC system can be heatintegrated with a cement manufacturing operation so that a reducedamount of additional fuel or even no additional fuel may be needed topreheat one or more of the MCFC inlet streams, such as all of the MCFCinlet streams. For example, the cathode inlet, which may comprise someCO₂ containing effluent from the kiln plus additional (cold) oxidant(air) to provide sufficient oxygen, can be preheated fully to typicalcathode inlet temperatures of about 500° C. to about 700° C. by heatexchange with kiln outputs. Additionally or alternately, the heat forthe kiln, typically provided by burning coal, can instead be partiallyor completely provided by burning anode exhaust effluent from the MCFCsystem, which, when derived from a less carbon-intensive source thancoal, can reduce overall CO₂ emissions.

In another additional or alternate configuration, the MCFC system can beconfigured to avoid a substantial majority of overall plant carbonemissions. In this configuration, the MCFC system anode outlet, a streamtypically containing CO₂, CO, H₂, and water, can undergo a series ofprocesses designed to separate CO₂ for sequestration/capture, to removewater in that same or in a different separation process, and/or to“shift” the water-gas shift gases to produce a stream highly enriched inhydrogen. This hydrogen stream can then be used as the heating input(when combusted) for the kiln, yielding reduced or minimized carbonemissions. Optionally, any off-gasses containing fuel value can berecycled to the anode (for example, a CO containing off-gas). Furtheradditionally or alternately, water from the anode exhaust can be used tooff-set any water used in the grinding, mixing, or other cementprocesses that might be drawn from local sources. The electricity neededfor at least a portion of or the entire cement, concrete, and/or quarryoperations, and/or for at least a portion of the operations, can beprovided by the MCFC on-site. This can reduce or minimize transmissionlosses as well as reducing corresponding CO₂ emissions from the fuelsused to provide electricity via the electrical grid. The overall processcan then exhibit “life-cycle” CO₂ emissions that can be substantiallyreduced, when compared to conventional mining and manufacturingoperations, while operating at higher overall thermal efficiency.

In these configurations, the fuel for the inlet to the anode cantypically be provided by a source of natural gas, methane, and/or otherlight hydrocarbons, optionally along with off-gasses and/or other wastestreams containing some light fuel components and/or along withwater-gas shift components. The fuel to the anode may contain otherinert gases, such as nitrogen, in acceptable amounts, but preferablydoes not contain substantial amounts of oxygen, such as no intentionallyadded oxygen. The anode inlet may additionally or alternately includeand/or be derived from other hydrocarbonaceous materials, includingcoal, if these materials are first converted to a reformable fuel. Atleast a portion of the heat (perhaps even all the heat) required forthese conversions, and optionally for preheating the anode inlet, canadvantageously provided by heat exchange from contact with kiln exhaustgases or products. The heat exchange can be direct, and/or can beindirect through a heat transfer medium such as steam. Water (steam) forsuch heat exchange processes, and/or water used in other processesrelated to cement manufacture, can be provided at least in part usingwater produced by the anode chemical and electrochemical reactions afterseparation from the anode exhaust stream.

The cathode inlet stream can be derived at least in part from the kilnexhaust that can be rich in CO₂. This stream may contain dust, dirt,minerals, and/or other solid substances not suitable for introductioninto a MCFC. Such unsuitable substances can be removed with, forexample, filters. Additionally or alternately, typically cement plantscan contain systems to reduce, minimize, and/or substantially eliminateparticulate emissions from the kiln, and similar systems can be employedin a system that is integrated with a MCFC. The kiln exhaust and/orcathode inlet stream containing at least a portion of kiln exhaust maycontain some residual gases not harmful to the cathode. Examples of suchresidual gases can include nitrogen, oxygen, and/or other aircomponents, as well as optional minor amounts of impurity pollutantssuch as nitrogen oxides, when present at acceptable concentrations (forexample, such as less than about 100 vppm, or less than about 50 vppm,or less than about 25 vppm, depending on the impurity pollutant(s)). Thecathode can additionally or alternately require the use of fresh air toobtain a sufficient oxygen concentration. Preferably, the oxygenconcentration at the cathode outlet can be at least about the CO₂concentration at the cathode outlet, but oxygen concentrations of atleast about half the CO₂ concentration can also be acceptable.Optionally, the oxygen concentration at the cathode inlet can be atleast about the CO₂ concentration at the cathode inlet. In many MCFCsystems it can be necessary to burn some fuel to heat the cathode inletstream. However, for the configurations described above, heat exchangewith the kiln gaseous exhaust and/or solid product can provide at leasta portion of the heat, or substantially all of the heat, required toheat one or more of the cathode inlet streams. This can reduce,minimize, or possibly eliminate the need for combustion of fuel toprovide additional heat for the cathode inlet streams.

The anode outlet stream, in most traditional power-producing MCFCsystems, can typically be partially or fully recycled to the cathode toprovide CO₂ and heat. In these configurations according to theinvention, this anode exhaust is not required for those purposes,instead optionally but preferably being used for another purpose, suchas to provide heat for the kiln. Advantageously, the MCFC can beoperated at reduced fuel utilization such that the anode exhaust, whenused either with or without shift and/or separation steps, can provideat least a portion (or all) of the heat necessary to raise the kiln tothe operating temperature. Advantageously, the conditions canadditionally or alternately be chosen such that the total electricalpower output can be sufficient for at least a portion (or all) of thelocal power needs, which may include the direct cement manufacture aswell as associated concrete, quarry and other operations. The MCFCsystems can be designed such that, by varying the fuel utilization, thesystem can meet both requirements and can respond to variability inthose requirements through adjusting fuel utilization, cell voltage andcurrent, and/or other parameters.

The cathode exhaust stream, typically comprising a reduced CO₂ and O₂concentration relative to the cathode inlet stream, along with inert(air) components such as nitrogen, can typically be exhausted to theatmosphere, but alternately can be first exposed to one or morepost-treatments before doing so.

FIG. 17 shows an example of an MCFC system integrated in a cementmanufacturing plant to produce low CO₂ emissions cement. The two largestCO₂ sources of a cement plant are typically from the combustion offossil fuels for heat in the kiln, such as a rotary kiln, and thedecomposition of CaCO₃ to CaO in the kiln. In the configuration shown inFIG. 17, the integrated process can instead combust H₂ produced from theMCFC in the kiln. The decomposition CO₂ off gas can additionally oralternately be used as the cathode feed.

In the configuration shown in FIG. 17, gas flows of methane 1701 andsteam 1702 can be fed to the anode of MCFC 1720. The anode exhaust 1703,which can comprise a mixture of H₂, CO, CO₂, and H₂O, can be cooled in aheat recovery steam generator (HRSG) 1722 and shifted in a water gasshift reactor (not shown), producing a mixture of mostly H₂ and CO₂1704. Stream 1704 can, in this case, be dehydrated 1760 and separated1750 into H₂-containing stream 1706 and CO₂-containing stream 1707.Stream 1707 can be compressed (and sold for use, shipped for useremotely, etc.) and/or can be sent to a sequestration facility. Stream1706 can be used as fuel for the open flame (along with oxidant/air1741) in the rotary kiln 1740. The “clinker” product formed in kiln 1740can be passed into clinker cooler 1770. Various types of heat exchangecan be performed with the kiln 1740, the clinker product, and/or theclinker cooler 1770 to provide heat for other processes in the system.In the kiln 1740, as CaCO₃ decomposes, CO₂ can be released. The CO₂ cancombine with the flame exhaust gases and exit the top of the kiln 1740as a kiln off gas 1708. The kiln off gas 1708 can be cleaned and/ordehydrated 1730 to form a water and/or impurities stream 1709 and aCO₂-containing stream 1710 that can be returned to the front of thecathode of MCFC 1720. Stream 1710 can be mixed with air 1711 andoptionally part of the cathode exhaust 1712 to help meet the CO₂ feeddemand to the cathode. The cathode exhaust, depleted in CO₂, can besplit, with a fraction optionally recycled 1712 and another fractionsent to a HRSG 1724 and emitted to the atmosphere 1713 (if not sent forfurther processing, not shown).

As an example of the heating requirements and CO₂ production from arotary kiln, values were taken from Energy and Emissions from the CementIndustry. (Choate, William T. Energy and Emissions ReductionOpportunities for the Cement Industry. U.S. Department of Energy,December 2003.) Based on these representative values, calculations wereperformed for an example of an integrated process sized to process ˜300tonnes/hour of clinker in the rotary kiln. Flow values based on mass andenergy balance calculations for a configuration similar to FIG. 17 areshown in the tables in FIG. 18. In FIG. 18, the number at the top ofeach column indicates the corresponding element from the configurationin FIG. 17. The calculations can be used to show that the large amountof heat in the clinker cooler 1770 shown in FIG. 17 can be used topre-heat all the MCFC inlet streams to operating temperatures. Inaddition to H₂ fuel for the kiln, the MCFC can also produce ˜176 MW ofpower that can be used in the other energy intensive processes, likegrinding of the raw material for the kiln feed. Table A shows a summaryof the additional electric power generation and reduced CO₂ emissionsthat were calculated based on the calculations shown in FIG. 18. Asshown in Table A, the calculations for a configuration similar to FIG.17 using representative values for the rotary kiln show that integrationof a MCFC with a cement process can provide additional electrical powerwhile reducing CO₂ emissions by about 90%.

TABLE A Power Generation and CO₂ Emissions during Cement ProcessingPower Generation CO2 Emissions [MW] [kg CO2/tonne Clinker] Fossil fuelfired kiln 0 976.5 MCFC + kiln 172 96.9

As noted above, about half of the CO₂ emissions from a typical cementprocess are due to combustion of fuels to provide heat for a kiln. Suchcombustion processes usually use air to provide a source of oxygen,resulting in off gasses from combustion that are relatively dilute inCO₂ concentration due in part to the large amount of N₂ present in air.The conventional alternative for separating CO₂ from a stream containingdilute CO₂ (such as 10 vol % CO₂ or less) is to use an amine wash, suchas an amine wash based on monoethanolamine. For comparison purposes, atypical expected energy cost for using an amine wash based onmonoethanolamine (MEA) to capture CO₂ from dilute CO₂ streams (such asstreams with approximately 10 vol % or less CO₂) was estimated to beabout 3 GJ/ton CO₂. Based on this expected energy cost, using an aminewash to capture CO₂ instead of using a MCFC could eliminate theadditional electrical energy generated by the MCFC while also incurringa substantial energy cost.

Integration with Iron or Steel Manufacture

In various aspects, processes are provided that integrate the productionof iron and/or steel with the use of an MCFC system. Iron can beproduced from the reduction of iron oxides present in iron ore. Thereaction can require high temperatures, such as up to 2000° C., moretypically from about 800° C. to about 1600° C., and a reductant that canremove tightly bound oxygen from iron oxide that can be used in theblast furnace to produce iron metal. The most widely used methodinvolves the processing of coal to produce coke and subsequently toproduce a blast furnace gas comprising CO as the primary chemicalreductant. The process can typically also require a substantial amountof heat, and frequently significant amounts of electricity used both inthe basic process itself, and in subsequent steel-making processing. Theelectrical requirements may include typical plant needs for operatingpumps, valves and other machinery as well as large, direct electricalinputs such as for direct-reduction iron processing, electric furnacesteelmaking, and similar processes. Substantial amounts of water can beneeded in steelmaking beyond the water simply used for cooling, as watercan be used to process coal, directly remove scale from steel, for steamgeneration, hydraulics and other systems.

In a conventional iron production process, the furnace gas can comprisea significant amount of CO, as well as some amounts of H₂, H₂O, N₂,optionally but typically sulfur (such as H₂S), and optionally buttypically one or more other various gases derived from coal. As iron canbe an effective water-gas shift catalyst, the four water-gas shiftmolecules (CO, CO₂, H₂O, H₂) can typically be at or near equilibrium inthe process. CO can react with iron oxides to produce CO₂ and reducediron, while incorporating some carbon into the reduced iron. This carboncan then be partially removed, for instance by controlled oxidation, tothe desired level for making various grades of iron and steel products.The role of the coal and coke in a conventional iron production processcan be two-fold. First, the coal or coke can provide the reductant forconversion of iron oxides to iron. Second, coal or coke can be combustedto provide heat to maintain the very high furnace temperatures. Theprocess can typically take place at or near atmospheric pressures. In aconventional process, effluent blast furnace gas still can typicallycontain some amounts of combustible materials that can then be burnedfor additional heat.

Disadvantages of conventional processes can include the production oflarge quantities of CO₂ for every ton of iron or steel produced. Inaddition to the coal and coke used in a process, a flux (typically acarbonate such as CaCO₃ or mixture of carbonates and other materials)can be decomposed in the process releasing additional CO₂. To capture orreduce the amount of CO₂ emanating from the furnace can requireseparation of CO₂ from the various exhaust systems which can bedifficult, and which can involve a number of collection, concentrationand clean-up steps.

In various aspects, integrating operation of molten carbonate fuel cellswith processes for iron and/or steel production can provide processimprovements including but not limited to increased efficiency,reduction of carbon emissions per ton of product produced, and/orsimplified capture of the carbon emissions as an integrated part of thesystem. The number of separate processes and the complexity of theoverall production system can be reduced while providing flexibility infuel feed stock and the various chemical, heat, and electrical outputsneeded to power the processes.

In additional or alternate aspects, the combined MCFC and ironproduction system can allow for efficient collection of carbon withsimpler systems while providing flexibility in heating. Additionally oralternately, the combined MCFC and iron production system canincorporate direct production of electricity that can be utilized aspart of the entire electrical input to the plant. As the electricity isproduced on-site, transmission losses can be reduced or minimized andpotential losses produced when converting AC to DC power canadditionally or alternately be avoided. Furthermore, the carbon in thefuel utilized to produce electricity can be incorporated into the samecarbon capture systems used for capture of carbon dioxide from the blastfurnace exhaust (or exhaust from another type of furnace used for ironor steel production). The proposed system can be designed for variableproduction of reductant (CO), heat, and electrical output, allowing itto be adapted to a broad range of iron and steelmaking processes andtechnologies using the same core components.

In an aspect, an MCFC system can be used to form an anode exhaust streamcontaining excess H₂ and/or CO (syngas). The excess syngas from the MCFCanode exhaust can be withdrawn and used to perform iron or steelproduction while reducing, minimizing, or eliminating the use of coke.The anode exhaust from the MCFC can be exhausted at a pressure of about500 kPag or less, such as about 400 kPag or less, or about 250 kPag orless. For example, one can take syngas produced or withdrawn from theanode exhaust, separate at least a portion of the H₂ from the CO, firethe furnace with the H₂, perform the reduction of iron with the CO, andthen consume the resulting CO₂ from the iron production process in theMCFC and capture it, leading to a substantial reduction in CO₂ emissionsfrom the process. In such aspects, the MCFC can act as both a managementsystem for carbon oxides (source of CO, sink of CO₂) and as a source ofsupplemental inputs to the iron or steel production process, such as byproviding H₂ for heating, heat exchange with input and exhaust streamsfor efficiency, carbon capture, and/or clean process water creation. Itis noted that various steel processes can additionally or alternatelyuse electrical energy that can be provided by the MCFC system. Forexample, steel production can involve the use of arc furnaces, anddirect reduction of iron can be done with electrical current. In variousaspects, the furnaces used in an integrated system including an MCFC canbe electrically heated or heated by other indirect methods that cangenerally allow combustion of the syngas in the furnace to be avoided.

As an example of integration of molten carbonate fuel cells in areaction system for producing iron or steel, the reductant gas to ablast furnace can be provided by first introducing methane or otherreformable fuel into an MCFC anode where the MCFC can be used to produceboth electricity (such as for use by the plant) and syngas from theanode output. The MCFC system can preferably be sized such that theamount of syngas produced can be sufficient to provide all orsubstantially all of the CO reductant needed for the iron or steelmaking process. Optionally, a portion of the CO for the iron or steelmaking process can additionally or alternately be introduced as part ofthe iron ore or other iron oxide feed to the furnace. Depending on thetypes of processes involved, which may require larger amounts ofelectricity (for example, in a direct reduction steel making process) orsmaller amounts of electricity, electricity may be returned to grid ordrawn from the grid, to balance the energy inputs from the plant.Alternatively, the MCFC can be sized so that it can produce both all theelectrical energy and reductant needed, with the MCFC being operated ata fuel utilization that balances the two main outputs to suit the plantrequirements. The flexibility of the system can allow for adjusting thisratio (by adjusting fuel utilization, voltage, and/or input/outputtemperatures, among other variables) to adapt to changing processes orprocess conditions within a given plant.

Optionally but preferably, an MCFC system integrated with iron or steelproduction can be operated at low fuel utilization, to increase theamount of syngas available to be produced/withdrawn from the anodeexhaust. While this may not be necessary, as most MCFC operations cantypically produce an anode effluent comprising syngas, it can sometimesbe preferable to maximize the production of anode syngas. For example,the fuel utilization can be at least about 25%, such as at least about30%, or at least about 35%, or at least about 40%. Additionally oralternately, the fuel utilization can be about 60% or less, such asabout 55% or less, or about 50% or less, or about 45% or less, or about40% or less. Use of a low fuel utilization value can allow for anincreased content of H₂ and CO in the anode output. The anode output canthen be used as a source of reducing gas for the blast furnace. Ifdesired, the fuel utilization can be adjusted so that the syngas outputcan be in balance with the electrical requirements of the overall plant.This can potentially avoid the need for separate grid-power and canprovide energy self-sufficiency to the plant with only a single fuelsource feeding a single power production system; the MCFC in such asituation could provide both the electrical and chemical constituentsneeded for plant operations. Alternatively, the plant may utilize aseparate electrical generation system such as a turbine in conjunctionwith an MCFC system, such that some electrical power can be produced byboth systems, and so that the MCFC system can be optimized for syngasproduction. The size, available fuel sources, intrinsic electricaldemand and other factors may result in any of these combinations beingan (the most) efficient and/or economically advantageous arrangement.

In various aspects, the fuel input for an MCFC in an integrated iron orsteel production system can preferentially comprise or be methane ornatural gas, but can indeed be any hydrocarbonaceous material compatiblewith an MCFC. For hydrocarbonaceous materials that cannot be directlyreformed within the MCFC (e.g. C2-C5 light gases), a pre-reformer can beemployed to convert the input fuel to methane plus a syngas mixture. Insuch situations, preferably the anode input gas can contain a large orpredominant percentage of a reformable gas and may contain amounts ofsyngas constituents and inerts. The anode input can preferably haveimpurities such as sulfur removed, which may be accomplished byconventional systems, and which can vary depending on the source andpurity of the input fuel. Input fuels such as coal and/or other solidfuels can be used, if first converted to mixtures comprising reformablefuels from which impurities are removed. Inputs to the cathode can bederived primarily from iron reduction process exhaust and may containother streams containing one or more of CO₂, H₂O, O₂, and inerts.Air/oxygen containing streams may be added to provide sufficient oxygenfor the cathode and can typically require oxygen amounts in the overallcathode exhaust to be in excess of the total CO₂ amounts.

Syngas effluent from the anode outlet can be sent to a separationprocess where CO₂ and possibly some water can be removed from thestream. The separation system can be designed to remove enough H₂O andCO₂ to produce a syngas composition that, when equilibrated in the ironreduction process conditions in the blast furnace, can have anappropriate amount of CO relative to other gas components. As opposed toconventional processes, the CO produced can be largely free fromimpurities such as sulfur, simplifying the need for pollutant controlsystems around the overall iron or steel-making plant which wouldnormally be required when utilizing coal and/or coke. After theconsumption of CO in the iron reduction process, CO₂ can be produced inthe effluent from the process. This CO₂-enriched effluent stream canthen be used as the input to the MCFC cathode, after appropriate heatexchange if desired. This can typically involve steam generation, whichcan then feed secondary electricity production from a steam turbine. Forexample, the effluent gas may contain combustible materials which canthen be burned to produce further heat by the addition of air or oxygen.The heat produced can be used in various plant processes, but the CO₂produced by the combustion can remain in the flue gas, which, whensubsequently introduced into the cathode, can be concentrated/capturedeffectively by the MCFC system.

Separate combustion of fuel for heating the MCFC system can be reducedor minimized in any of the above systems, as sufficient waste heat forheat exchange should typically be available from the iron or steelproduction processes. Preferably, lower fuel utilization can beemployed, as operating under such conditions can produce higher COproduction per fuel cell array employed and greater carbon capture perMCFC array employed. The blast furnace off gas can additionally oralternately be heat integrated with the MCFC inlet/outlet. A portion ofthe blast furnace off gas can be used as at least a portion (orpotentially all) of the cathode feed, while the remainder of the blastfurnace off gas can be emitted to the atmosphere and/or compressed forCO₂ sequestration in a low CO₂ emissions iron or steel productionscheme.

In another embodiment, the H₂ and CO can be separated after productionby the anode, and the H₂ can optionally but preferably be used toprovide carbon-free heating for the various plant processes, while theCO can optionally but preferably be used in the iron reduction. This canallow for fewer CO₂ sources within the overall plant and may simplifyCO₂ collection for introduction as cathode feed gas.

An advantage of the MCFC system over conventional carbon capturesystems, such as amine capture, can include a lack of criticality forthe CO₂ separation system to capture a relatively high percentage (e.g.at least about 90% or at least about 95%, by volume) of the CO₂ from theanode. As opposed to conventional capture technologies, any carbon (asCO or CO₂) not captured can be converted to CO₂, recycled from the ironreduction process to the cathode inlet, and then (typically) mostlyconverted to carbonate ions to be transported across the MCFC membraneto the anode, where they can undergo the CO₂ separation process. Theonly CO₂ emission from the system in such a configuration can come fromthe cathode exhaust. The overall CO₂ capture efficiency of the plant canbe adjusted based on the ratio of the cathode out CO₂ concentrationrelative to the cathode input CO₂ concentration, which can be easilyvaried, such as by adjusting the number of operation stages of the MCFCarrays and/or by adjusting the number of MCFC cells to increase theavailable fuel cell area.

FIG. 19 shows an example of a configuration suitable for operatingmolten carbonate fuel cells (MCFCs) in conjunction with an ironreduction process. The FIG. 19 configuration can be suitable forreducing iron oxides, such as Fe₂O₃ and/or other iron oxides found invarious types of iron ore, to pig iron (about 95% Fe). In FIG. 19, steam1901 and pre-heated methane 1902 can be fed to the anode of the MCFC1940. Optionally but preferably, the methane 1902 can be pre-heated viaa heat exchanger 1991 by recovering heat from stream 1907 derived fromthe blast furnace off gas. The MCFC 1940, such as an MCFC operating atabout 30% fuel utilization, can produce reducing gases (e.g., CO and H₂)in the anode exhaust 1903 that can be sent to the blast furnace. Anodeexhaust 1903 can optionally but preferably be heated, e.g., byrecovering some of the heat from the blast furnace off gas 1906 in heatexchanger 1992. The heated anode exhaust 1904 can be heated to the blastfurnace inlet gas temperature (for example about 1200° C.) in pre-heater1993, resulting in an inlet gas stream 1905. Conventional methods can beused for introduction 1952 of solid particles of iron oxides into thetop of the blast furnace 1950. Optionally, the input flow 1952 ofparticles of iron oxides can be introduced along with a flux agent, suchas CaCO₃, that can assist with formation of a slag that can be readilyseparated from the iron product. The input flow 1952 of particles ofiron oxides can flow through the blast furnace 1950 counter current tothe reducing gas 1905, which can enter the blast furnace 1950 at alocation typically more toward the bottom. Reduced Fe can leave thefurnace as a bottoms flow 1956, while a furnace off gas comprising CO₂and H₂O can leave the furnace as 1906. Furnace off gas 1906 can beintegrated with the process to heat the anode exhaust 1903 in heatexchanger 1992 and/or pre-heat anode input flow 1902 in heat exchanger1991. These heat recovery processes can result in a cooled furnace offgas stream 1908. Optionally, further heat can be removed from furnaceoff gas stream 1908 using a heat recovery steam generator (HRSG). Watercan be condensed from the cooled off gas stream 1908 in condenser 1994,producing process water 1909 and a gas 1910 with a relatively highconcentration of CO₂. Gas 1910 can optionally also contain some methane.A fraction of gas stream 1910 can be split off as a feed stream 1912 toa burner and can be burned using an oxidizing source (air) 1913 and afuel (methane) 1914 to produce enough CO₂ at an appropriate temperaturefor the cathode feed 1915. The remainder of gas 1910 can be sent 1911 toa CO₂ separator/compression system, for instance to produce pipelinequality CO₂ for use and/or sequestration or alternately to be emitted tothe atmosphere. Some heat from burning streams 1912, 1913, and 1914 canadditionally or alternately be used to heat stream 1904. A heat recoverysteam generator (HRSG) can be used to remove any additional heat in 1915before it is sent to the cathode and to generate steam for thedownstream steel manufacturing processes. The MCFC can remove aconvenient or desired portion of the CO₂, for example, at least about50% or at least about 70% of the CO₂ in 1915, giving a reduced CO₂exhaust stream 1916. Exhaust stream 1916 can be emitted to theatmosphere and/or recycled back as part of cathode input stream 1915.

Example of Configuration for Integration of MCFC with Blast Furnace

This example demonstrates an integrated MCFC system with an iron blastfurnace, which reduced Fe₂O₃ to pig iron (95% Fe). The reaction systemconfiguration for this example was similar to the configuration shown inFIG. 19. In this example, the MCFC system was operated at 30% fuelutilization with a methane-steam feed to the anode to produce reducinggas for the blast furnace. The blast furnace off gas was heat integratedwith the MCFC inlet/outlet and a fraction of it can be used as thecathode feed, while the remainder can be emitted to the atmosphere orcompressed for CO₂ sequestration in a low CO₂ emissions iron/steelproduction scheme.

The integrated MCFC process was sized to produce enough reducing gas tooperate the blast furnace of a ˜2.8 Mton/year steel plant. In additionto generating the reducing gas feed for the blast furnace based on theanode exhaust, the MCFC also produced about 233 MW of power which couldbe used to power other parts of the steel plant, to power separation andcompression of CO₂ for pipeline transport (such as CO₂ stream 1911 asshown in FIG. 19), and/or to be sold back to the grid. FIG. 20 showsrepresentative values for the flow composition at various locations in asystem having a configuration similar to the configuration shown in FIG.19. For convenience, the stream designations shown in FIG. 19 were alsoused to designate the streams in FIG. 20. It is noted that thecomposition of anode output stream 1903 was based on a fuel utilizationin the anode of about 30%. The changes in the relative composition ofstreams 1904 and 1905 were due to equilibration via the water gas shiftreaction. It is noted that the composition of blast furnace off gas 1906was based on simulated consumption of ˜100% of the reducing gas in theblast furnace, while no methane was consumed in the furnace. In a realsystem, it is likely that an excess of reducing gas would be used toprovide process stability. Additionally, it is likely that a smallamount of methane would be consumed in the blast furnace via reactionwith previously reduced iron, potentially leading to introduction ofminor additional carbon into the iron as well as production ofadditional H₂. However, this idealized calculation of the composition ofblast furnace off gas 1906 provides representative values for the energycontent and composition.

It is noted that a conventional configuration for a similarly sizedsteel plant was reported in a journal article by Arasto et al. (Title:Post-combustion capture of CO₂ at an integrated steel mill—Part I:Technical concept analysis; Antti Arastoa, Eemeli Tsuparia, JanneKärkia, Erkki Pisilä, Lotta Sorsamäkia, International Journal ofGreenhouse Gas Control, 16, (2013) p. 271-277). The configuration inArasto et al. produced 135 MW with an HRSG-turbine system that recoveredheat from the traditional coal burners and blast furnace. This wasenough power to operate the ˜2.8 Mton/year steel plant, provideelectricity to a local community, and export some to the gird. Bycontrast, by using an MCFC for power generation on the methane feed, asopposed to generating power from the excess heat of the steel plant, theMCFC in this example generated about 233 MW of power. Compared to theconventional steel plant configuration reported in Arasto et al., theintegrated MCFC-blast furnace system can produce more power, and canalso reduce the CO₂ emissions by at least 65%.

Integration of MCFC with Refinery Hydrogen Use and “Carbon-Free”Hydrogen

Hydrogen can be used within the refinery for a variety of processes.Most refineries both generate hydrogen in some processes (for example,gasoline reforming to produce aromatics) and use hydrogen for otherprocesses (for example, sulfur removal from gasoline and diesel blendingstreams). Additionally, refineries can have a large number of boilers,furnaces and/or other systems for heating reactors that require energy.These heating and/or energy generation systems generally do not utilizehydrogen, because hydrogen can typically be more valuable than otherfuel sources, and because most refineries are, on an overall basis, netimporters of hydrogen. Generally, hydrogen import can be done bybuilding on-site, and/or by accessing nearby/pipeline sources ofhydrogen to bring the overall refinery into balance.

Since most refinery processes typically take place at elevatedtemperature and usually require heat provided by boilers of varioussorts (as well as process steam), refineries generally contain largenumbers of heating systems. This can result in a large number of pointsources of CO₂ that can vary widely in size. Some, like cat cracking,can produce large amounts of CO₂, while others can produce modestamounts. Each of these point sources of CO₂ can contribute to theoverall refinery CO₂ production. As most integrated refineries aretypically about 70-95% thermally efficient on an overall basis atconverting crude oil to products, typically about 5-30% of the carbonentering the refinery in crude oil or other inputs can be exhausted (tothe air) as CO₂. Reduction of these emissions can improve refinerygreenhouse gas emissions per unit of product produced.

In various aspects, integration of an MCFC system with a refineryhydrogen supply can reduce, minimize, or eliminate hydrogen constraintson the overall refinery operation. Additionally or alternately, the MCFCsystem can use, as inputs, any of a wide variety of off-gasses and/orother streams, as long as they can be converted to “clean” light gassesand syngas mixtures. It is noted that the light gas and/or syngasmixtures can be used without much restriction on the amount of inerts(e.g., N₂, CO₂, and the like, and combinations thereof) present. This“input integration” can additionally or alternately be a feature instreamlining overall efficiency in refinery operation. More generally,an MCFC system can provide a single integrated solution for up to four(or potentially more) aspects of refinery operation: production of heatfor process units, production of hydrogen as a reactant, collection andsequestration of carbon, and efficient utilization of off-gases andpurge streams from various processes.

In some aspects, H₂ can be used as the fuel in burners in a refinery toreduce, minimize, or eliminate CO₂ emission point sources. A centralizedsupply of H₂ for both purposes can simplify overall refinery operationsby reducing the number and type of fuels and reactants—only one materialcan be distributed for these purposes. For example, hydrogen can be usedat a variety of temperatures and pressures. An MCFC system can producehydrogen from the anode exhaust stream after (optional) separation ofwater and CO₂, and further (optional) purification through anyconventional method, such as pressure-swing adsorption. Once purified totypical refinery requirements, such as a purity (on a dry basis) of atleast about 80 vol % H₂, or at least about 90 vol %, or at least 95 vol% or at least 98 vol %, a hydrogen-containing stream can be pressurizedto an appropriate pressure for process use and piped/transported to anyprocess. The hydrogen-containing stream may be split into multiplestreams where lower purity and/or lower pressure streams can be sent tosome processes or burners, while higher purity and/or higher pressurestreams can be sent to other processes.

The integrated system can additionally or alternately, but typicallyadvantageously, produce electricity. The electrical production may beused to at least partially power MCFC-related systems, such asseparation systems or compressors, as well as to power at least aportion (such as up to all) of the refinery electrical demand. Thiselectricity can be produced at relatively high efficiency with little orno transmission losses. Additionally, some or all of the electricity canoptionally be direct current (DC) electricity, for instance where DCpower could be preferred for the operation of some systems without thenormal losses in transformers/inverters. In some aspects, an MCFC systemcan be sized so that at least a portion (or all) of the power needed bythe refinery can be provided, or even so that excess power can beprovided. Additionally or alternately, the MCFC system can be sized to adesired H₂/heat load and/or to the electrical load. Furthermore, thesystem can be operated over a range of conditions, allowing for variableamounts of both electrical and hydrogen demand.

At least a portion of the refinery processes that produce CO₂ can becollected and used as some or all of the gasses for the cathode inlet,such as a majority of the CO₂ production processes or all of the CO₂production processes. If necessary, these gases can be mixed with air orother oxygen containing streams to comprise a gas mixture with both CO₂and oxygen appropriate for the cathode inlet. Fuel constituents presentin these streams can typically be burned with excess oxygen/air toprovide preheating of the cathode inlet. The CO₂ concentration of theoverall cathode inlet can vary widely, and can typically be at leastabout 4 vol %, such as at least about 6 vol %, at least about 8 vol %,or at least about 10 vol %. If the collected streams do not containsufficient CO₂ concentrations for MCFC operations (or even if so), thenCO₂ produced in the separation of the anode exhaust and/or from one ormore off-gas or purge streams from the separation process can berecycled to the cathode inlet. Heating for the cathode inlet streams maycome from combustion of off-gases in these streams, heat exchange,and/or addition of combustible fuel components. For example, in someaspects the MCFC system can use high carbon materials, like coke orpetcoke, and/or other “bottoms” from petroleum processes, to provideheat for inlet streams where the combustion products from thosematerials can be used as a CO₂ source for the cathode.

Additionally or alternately, at least a portion of the CO₂ for thecathode inlet stream can be provided by a combustion turbine, such as aturbine that can use methane/natural gas as a fuel. In this type ofconfiguration, CO₂ generated by processes such as catalytic cracking maynot be mitigated, but CO₂ generated by heaters, boilers, and/or otherburners can be reduced or minimized by using H₂ generated by the MCFC.

The anode outlet stream can contain a large concentration of carbondioxide as well as other syngas components. Typically, CO₂ can beremoved from this stream efficiently to produce a CO₂ product that canbe used for a variety of other processes. As a significant fraction ofthe carbon dioxide produced from the refinery can exit from an MCFCanode, collection of CO₂ can be efficient and greatly simplified. Thecollection of CO₂ as a single point source can then be used for otheroperations (e.g., EOR if near oil fields, re-injection to gas wells)and/or can be captured/sequestered. The removal of a majority of theentire CO₂ load, such as at least about 70%, or at least about 80%, forboth H₂ production and electricity use, can substantially lower thegreenhouse gas impact of refinery operations and can improve overallrefinery efficiency (conversion of crude to products) by adding ahigh-efficiency source of electricity, hydrogen, and heat within asingle process.

In aspects where an MCFC system is integrated with the hydrogen deliverysystem in a refinery, the anode input for the MCFC system can beselected from a large variety of materials available from variousrefinery processes, such as light gasses pre-reformed to reduce C2+;methane; gasified heavy materials like gasified coke or bitumen; syngas;and/or any other hydrocarbonaceous material that can be cleaned ofsulfur and other harmful impurities; as well as combinations thereof.Thus, the MCFC system, with proper pre-cleanup, can act as a “disposal”for all sorts of inputs which might otherwise not have an efficient oreffective use in the refinery. Instead of eventually being exhausted tothe atmosphere, optionally after being burned as a fuel, a predominantamount of the carbon in these “waste”, “purge”, or other undesirablestreams can be effectively concentrated/captured as separated CO₂ by thesystem. The cathode input can be or comprise any refinery streamcontaining CO₂ off-gasses plus any recycle from the anode exhaust orburned fresh methane that might be used for heat exchange. Mostrefineries have a wide variety of processes operating at varioustemperatures, so appropriate refinery processes can be selected for someheat integration to manage, for example, clean-up cooling and heating.The cathode exhaust can generally be exhausted to the atmosphere. Theanode exhaust can be used as is, optionally after separation of somecomponents, and/or can undergo both separation and water-gas shift toproduce a stream that is nearly all H₂. The high H₂ content stream canbe purified to a desired level for various reactive processes, whilecombustion H₂ can contain greater levels of residual CO, CO₂, and soforth, as combustion of such a stream can still result in reducedemissions of carbon oxides relative to combustion of a hydrocarbonaceousfuel. CO₂ separated from the anode to exhaust can optionally berecycled, for example, for use as an input to the cathode. Additionallyor alternately, feeds to the anode can include those with large CO₂impurities such as natural gas with a large CO₂ content. For normalrefinery operations this type of stream could increase the CO₂ emissionsfrom the refinery when used for either heat or hydrogen generation. Whenfed to the anode of an MCFC system, however, the separation stage(s) caneffectively remove this additional CO₂ as part of removal of other CO₂in the anode exhaust.

An additional difficulty in capturing carbon from the disparate CO₂sources in a refinery can be the low concentration of the CO₂ oftenpresent in the refinery streams. In general, the energy required forseparation of the CO₂ from the gas stream is highly dependent on theconcentration of CO₂ in the stream. For processes that generate gasstreams with low CO₂ concentrations, such as CO₂ concentrations of about10 vol % or less, substantial energy can be required to separate CO₂from a stream to form a high purity CO₂ stream. By contrast, in someaspects, a feature of an MCFC containing system can be that CO₂ can betransferred from a relatively low concentration stream (such as acathode inlet stream) to a relatively high concentration stream (such asan anode exhaust). This can reduce the energy requirements for forming ahigh purity CO₂ gas stream. As a result, an MCFC can provide substantialenergy savings when attempting to form, for example, a CO₂-containingstream for sequestration.

Output electricity generated by the MCFC directly can typically be as DCpower, but can be configured to produce any convenient mix of DC and/orAC power at a variety of current and voltage settings. Typically, apower plant/input electrical for a refinery can be a common high voltageAC current (e.g. ˜960V). Due to the way molten carbonate fuel cells areconstructed, one can produce essentially any DC current/voltage and,with inversion, a variety of AC voltages. DC, produced locally, shouldnot suffer transmission losses typical of long-distance power lines andshould not require inverters, at considerable cost and some efficiencyloss. This can provide some flexibility in designing compressors, pumps,and other components and/or can eliminate a number of grid and/or localelectrical inefficiencies.

In addition to use within a refinery, hydrogen can be more generallyuseful for a wide variety of products and processes, as it produces onlywater vapor on combustion. However, most conventional approaches tomaking hydrogen require large emissions of carbon. For example,production of hydrogen from steam reforming of methane can typicallyproduce CO₂ (from the carbon in the methane) and waste heat. Productionof hydrogen from electrolysis can require electricity that can typicallybe derived from a mixture of fossil fuel production to the electricalgrid. These production systems can all result in effluent exhaustscomprising CO₂. The effluents, if carbon capture is required, wouldtypically entail separate carbon capture systems at those varioussources, without any convenient integration into wider refineryoperations. Typically, these sources can actually be outside of therefinery gates, allowing for little or no synergisticproduction/consumption of the various chemical, electrical, and heatinputs and outputs.

Additionally or alternately, MCFC containing systems according to theinvention can provide the means to separate CO₂ efficiently from theprocess as an integral part of the separation and hydrogen purificationsteps. The CO₂ can then be captured, and/or used for other usefulprocesses. This can occur at high overall system efficiency—far higherthan conventional means of producing net hydrogen export, especially atsmall scale and under variable load.

The use of a MCFC system for hydrogen production for use in subsequentprocesses that may generate electrical power or heat can allow forrelatively low-emission production at relatively high efficiency andwith low (minimum) carbon emissions. The MCFC system can dynamicallyrespond to varying needs for hydrogen by adjusting the ratio of chemicalenergy production to electrical energy production and can be ideal foruses where loads and demands may not be approximately constant—varyingfrom pure electrical production with no excess hydrogen to high hydrogenproduction. Furthermore, the integrated MCFC system can be scaled over awider range of applications with relatively high efficiency than largerscale systems such as methane steam reformers.

The MCFC-hydrogen production system can have an advantage thatrepurposing the hydrogen for fuel value can produce lower net CO₂emissions than conventional systems without carbon capture and canproduce far lower emissions with use of the inherent system CO₂separation. This can be valuable in a variety of applications. Hydrogencan be produced for fuel cell vehicles that can use low temperature/lowpressure hydrogen. The amount of hydrogen and electricity can be varieddepending on overall demand maintaining overall high system efficiency.Hydrogen for export into boilers and/or other combined heat and powersystems can allow for the constant production of electricity, e.g., instand-alone generation, along with a variable amount of carbon-free heatvia the production of hydrogen with subsequent combustion inheater/boiler and similar systems. For example, an installation couldproduce primarily electricity in the summer for air conditioning systemswhile switching to a mix of primarily chemical energy in the winter forheating operations. Other applications can include systems designed toprovide on-site hydrogen such as in laboratories and other technical andmanufacturing facilities where some hydrogen can be beneficial alongwith a need for electrical energy.

In aspects involving hydrogen production and/or electrical powergeneration, the anode inlet can be fed by fresh methane, anothersuitable hydrocarbon fuel, and/or the combination of fresh fuel andrecycled CO and/or H₂ from the various processes. The anode outletstream comprising H₂ and/or CO can provide the components to producehydrogen. This can typically be done through some combination ofreaction, separation, and purification steps. An example would be afirst stage employing water-gas shift to shift as much CO as possible toH₂ by the reaction H₂O+CO=H₂+CO₂, followed by a second (and subsequent)stage(s) that remove H₂O and CO₂ from the H₂, and provide a suitablepurity product. Such stages can include PSA, cryogenic separation,membranes, and other known separation methods, either individually or incombination. The off-gasses from these steps can be recycled and/or usedto provide heat for inlet streams. The separated CO₂ can be used as arecycle stream and/or can be captured and/or used for other processes.The cathode inlet can be composed of recycled CO₂ from the overallprocess and/or CO₂ produced by the combustion of fresh (or recycled)fuel used to provide heat to the inlet streams. The cathode effluent cantypically be exhausted to the atmosphere, optionally but preferablyafter heat recovery to, for example, provide heat for other processstreams and/or in combined cycled electrical production, though thecathode effluent could optionally but less preferably be sent forfurther treatment, if desired.

MCFC systems integrated into carbon-free heat and power applications canbe used over a range of operating conditions ranging from fuelutilizations with lower hydrogen make (e.g., 60-70%) to lower fuelutilizations (e.g., 20-30%) for high hydrogen production. The exactoperational range of an individual application may vary widely both byapplication and over time. The ability to adapt to this operationalrange can be a desirable advantage. The number of separation stagesand/or the purity achieved can depend on the ultimate application.Simple production of hydrogen for low-emissions heat can be tolerant tomodest impurities in the hydrogen, as even a few percent CO₂ and/or COcould still result in very low overall emissions. High purificationapplications such as fuel cell vehicles and/or hydrogen for laboratoriesmay require multiple steps (e.g. cryogenic separation followed by PSA)to achieve purity specifications.

As an example of providing hydrogen to multiple refinery processes, anMCFC can be operated to generate electricity and an anode exhaust thatcontains H₂, CO₂, and H₂O. One or more separations can be used toseparate CO₂ and/or H₂O from the anode exhaust (or alternatively from agas stream derived from the anode exhaust). This can result in a firstgas stream having an increased volume percent of H₂ relative to theanode exhaust. A separation can then be performed on the first gasstream to form a second gas stream with an even higher volume percentageof H₂ than the first gas stream. The remaining portion of the first gasstream can then be compressed to a first pressure for use in a processwith less stringent requirements for hydrogen, while the second gasstream can be compressed to a second (higher) pressure for use in aprocess requiring a higher pressure and/or higher purity hydrogen input.

Example—Integration of MCFC with Refinery Hydrogen Supply

In the following example, calculations were performed for aconfiguration where an MCFC system was used as a source of hydrogen forsupplying various burners, boilers, and/or other units that usecombustion of a fuel as a source of energy. While the following examplesfocus on supplying hydrogen to combustion reactions, the hydrogengenerated by the MCFC could additionally or alternately be used tosupply one or more processes (such as a plurality of processes) wherehydrogen can be used for a purpose other than combustion. For example,the hydrogen generated by the MCFC could be used in one or morehydroprocessing reactors within a refinery.

In the following example, the CO₂ for the cathode was calculated basedon using an external source of CO₂. This choice was made for conveniencein demonstrating the energy benefits of using an MCFC for reducing CO₂emissions in comparison with attempting to capture CO₂ via anothermethod, such as using conventional amine washes for each potential pointsource of carbon. For comparison purposes, a typical expected energycost for using an amine wash based on using monoethanolamine (MEA) tocapture CO₂ from relatively dilute CO₂ streams (such as streams withapproximately 10 vol % or less CO₂) was approximated to be about 3GJ/ton CO₂. A substantial portion of this energy cost can be avoided byusing an MCFC to concentrate CO₂ in an anode exhaust stream. It is notedthat, in embodiments where CO₂ is collected from various point sourceswithin a refinery for use as part of the cathode input, some additionalenergy cost may be required to deliver the CO₂ streams to the MCFC.However, those costs can be at least approximately or roughly offset (ifnot exceeded) by the additional energy inefficiencies required for aconventional configuration where a separate amine wash would need toincur similar costs for delivery of CO₂ to a central amine wash, and/orby the additional energy inefficiencies that would be incurred by havinga separate amine wash for each point source of CO₂.

The following configuration examples provide two alternatives foroperating an MCFC to provide hydrogen for consumption in a refinery. Inthe calculations for the first configuration, a gas turbine was used togenerate electricity and to provide a source of CO₂ for the cathodeinput. In the calculations for the second configuration, additionalmethane was burned to provide the heat and CO₂ for operating the fuelcell. In both configurations, the anode exhaust was processed in one ormore separation stages to separate CO₂ (such as for sequestration) fromH₂ (used for fuel in the refinery).

In these examples, calculations were performed for supplying the heatrequirements of a typical refinery that can process about 500 kbd ofcrude oil. A refinery with a refining capacity of about 500 kbd can useabout 118 Mscf/d (or roughly 3.34×10⁶ m³ per day) of natural gas to theheating system, which can produce roughly 118 Mscf/d of CO₂ emissionsfrom combustion, if no capture/sequestration mechanism is used. Thefollowing examples integrate a MCFC process with a refinery gas firedheater system in a roughly 500 kbd system to provide distributed heatingwith low CO₂ emissions.

FIG. 21 schematically shows an example of a system for integratedprocessing with a combustion gas turbine, MCFC system, and refinery widefired heaters that burn

H₂. The system in FIG. 21 is configured such that the turbine cangenerate the CO₂ feed required in the cathode to produce enough H₂ inthe MCFC system to run the refinery heating system. Air 2101 and methane2102 were fed to a combustion gas turbine 2150 and burned to produce ahot cathode feed 2103. The excess heat in hot cathode feed 2103 was usedto pre-heat the anode methane feed 2104, which can then be fed 2105 tothe cathode of MCFC 2140. Anode methane feed 2104 and steam 2106 werefed to the anode of MCFC 2140. The MCFC can produce a low CO₂ contentcathode exhaust 2107 at high temperature. Depending on the aspect, theMCFC can be operated at a low fuel utilization (e.g., of about 25% toabout 60%, such as a fuel utilization of at least about 30%, or at leastabout 40%, or about 50% or less, or about 40% or less). Additionally oralternately, the MCFC can be operated at a more conventional fuelutilization (e.g., of about 70% or greater, though conventional fuelutilization can typically be between 70% and 75%), but this can be lesspreferable, as the amount of potential H₂ that capable of beingrecovered from the anode exhaust can be reduced. Heat can be recoveredfrom cathode exhaust 2107 in a HRSG (Heat Recovery Steam Generationsystem) before the cathode exhaust is emitted to the atmosphere (orfurther processed). The anode exhaust 2108 can be cooled in a HRSGand/or can be shifted in a water gas shift reaction stage 2160. Theshifted gas 2109, mostly H₂ and CO₂, can go through a separation unit2170 to produce a CO₂ stream 2110 and a H₂ stream 2111. The CO₂ stream2110 can be compressed and sold for use and/or sequestered. H₂ stream2111 can be distributed to the refinery heaters as the heating fuel.Each sub-stream of H₂ stream 2111 can be burned with oxidant (air) 2112in burners 2180 that can be located at one or more locations in therefinery to provide heat with substantially no CO₂ emissions. For aconfiguration similar to FIG. 21, FIG. 22 shows representative valuesfor the flow volumes within the configuration.

FIG. 23 schematically shows another example of a system for integratedprocessing with an MCFC system and a refinery fired heaters with methaneand hydrogen burners. This system was configured such that the methaneburners can generate the CO₂ feed required in the cathode to produceenough H₂ in the MCFC system to run the remaining hydrogen burners.Methane 2301 and oxidant (air) 2302 can be distributed to the methaneburners 2390. The off-gas 2303 can be collected from the methane burnersand sent to a feed pre-heater 2345. Methane 2304, oxidant (air) 2305,and off-gas 2303 can be burned in pre-heater 2345 to produce a hotcathode feed 2306. The excess heat in 2306 can be used to pre-heat theanode (methane) feed 2307 and fed to the cathode at 2308. The pre-heatedmethane 2309 and steam 2310 were fed to the anode. The MCFC 2350 canproduce a low CO₂ content cathode exhaust 2311 at relatively hightemperature. Heat can be recovered from cathode exhaust 2311 in a HRSG,e.g., before it is emitted to the atmosphere or sent for furthertreatment (not shown). The anode exhaust 2312 can be cooled in a HRSGand shifted in 2360. The shifted gas 2313, mostly H₂ and CO₂, can gothrough a separation unit 2370 to produce a CO₂ stream 2314 and a H₂stream 2315. H₂ stream 2315 can be distributed to the hydrogen burners2380. Each sub-stream can be burned with oxidant (air) 2316 in burners2380 that can be located at one or more locations in the refinery toprovide heat with substantially no CO₂ emissions. For a configurationsimilar to FIG. 23, FIG. 24 shows representative values for the flowvolumes within the configuration.

Based on configurations similar to FIGS. 21 and 23, and based on processflow similar to FIGS. 22 and 24, the relative net power production wascalculated for sequestering carbon for a refinery integrated with anMCFC. This was compared with a calculation for the net power productionfor a conventional refinery system where amine wash systems were usedfor carbon capture for each point source. As noted above, it has beendetermined that using a representative amine wash (e.g., with MEA) tocapture CO₂ from a typical dilute refinery stream (such as streamscontaining about 2 vol % to about 8 vol % CO₂) can require about 3GJ/ton CO₂. Table 2 shows the comparison for the inventiveconfigurations similar to FIGS. 21 and 23 (which can result in CO₂streams such as stream 2110 or stream 2314) relative to a conventionalamine wash method. For the comparison in Table 2, the % CO₂ emissionreduction represents the percentage of carbon that passes through theanode of the MCFC. Based on the calculated values shown in Table 2, useof an MCFC to provide H₂ for refinery burners and to centrally separateCO₂ can result in additional available power being generated. This cannotably be in contrast to the substantial power requirements forseparating CO₂ using a conventional configuration.

TABLE 2 Carbon Capture and Net Power Generation Configuration 1Configuration 2 % CO2 emissions reduction 55.98% 86% Net power with MCFCpower [MW] 110 36 Net power with MEA capture [MW] −115 −180Low Temperature Combustion Exhaust Sources Integrated with MCFC Systems

Low temperature combustion exhaust sources can comprise any streamcontaining CO₂ and O₂ (or possibly just CO₂ with addition of air) thatrequires cooling before use in a fuel cell. Generally this can be adirect result of having some pollutants (e.g. sulfur, metals) that wouldpoison the Ni catalyst on the cathode. For these purposes, small amountsof NOx or SOx are typically not considered a poison for the cathode Nicatalyst. For combustion exhaust sources containing elevated levels ofpollutants, the original combustion effluent needs to be cooled to atemperature where the impurities can be removed, then reheated via heatexchange, e.g., with cathode effluent, to the MCFC operationaltemperature.

Examples of low temperature combustion exhaust sources can includecoal-fired combustion sources, like coal power plants and lignin firedcombustion such as from wood and other biomass combustion. Other “dirty”fuels might include heavy fuels derived from petroleum like bunker fuelor other heavy marine fuels where there are enough impurities to needclean-up.

The combined system can offer the ability to do multiple operations morecleanly than would otherwise be possible. For example, lignin (e.g. fromcellulosic ethanol production) can be burned to make CO₂, heat exchangedso that it is cool enough to remove impurities, and then the CO₂ streamcan be combined with the CO₂ off-gas from fermentation as the cathodeinlet. This CO₂ then produces (along with methane in the anode) theelectrical power to power the plant's operations, and the residual heatto power other reactors which, for biofuels, would be at lowertemperature. Residual CO₂ can be separated/captured, which then improvesthe overall emissions from the plant. For a ship-board system usingheavy fuel oil, the core electrical power for the ship can be providedalong with heat and by default, a much cleaner total exhaust (eventhough the CO₂ would be emitted). For coal combustion the benefits canbe based on the potential for reduction of CO₂ emissions, although theability to produce excess syngas for this (and other cases) can also beused as a combustion aid in the prime combustion of the “dirty”material. In such aspects, the H₂ or H₂/CO used as a combustion aid canimprove the combustion characteristics of a lower quality fuel, allowingfor cleaner/more efficient burning in the first place. Additionally, theexcess syngas as H₂ can be used in clean-up operations for the materialup front (e.g. hydrodesulfurization) providing the necessary ingredientwithout actually building any additional equipment.

The cathode input can be the combustion source after cooling,contaminant removal, and reheating via heat exchange. Some of theup-front clean-up of the material to be combusted may be done viahydrogen treatment where the H₂ is derived from the MCFC. The cathodeinput can be supplemented with either fresh methane burned at leanconditions or, if more O2 is needed, air. The cathode output can beexhausted to the atmosphere. The anode input can be methane, naturalgas, or another reformable fuel, but could also be augmented bypartially gasified material (gasified biomass or coal), and pre-reformedlight hydrocarbons if present. The H₂ in the anode exhaust can beseparated and/or recycled.

Integration with a Hydrogen Turbine

In some aspects, an objective in producing low-carbon power can be toincrease or maximize the total power output while maintaining high CO₂capture efficiency and/or while efficiently utilizing existing systems.In a conventional system, a gas turbine can be connected to a MCFCsystem such that the gas turbine produces an exhaust stream comprisingCO₂ that serves as a component of the cathode inlet providing heat andCO₂ to the cathode. For this configuration, as is known in theliterature, CO₂ can be captured by conventional means and the MCFCsystem can be operated at relatively high fuel utilizations (typicallyabove 70% to about 80%, or about 75%) to maintain heat balance withinthe MCFC under ordinary operating conditions.

The efficient utilization of the MCFC can be improved by lowering thefuel utilization to process excess fuel, for example methane, andproduce excess syngas as an exhaust. This exhaust/effluent can undergovarious separations to yield a syngas stream that can be useful for avariety of chemical and industrial purposes. However, where syngas isnot useful as a feed stock, and/or for cases where electrical powergeneration can be a primary goal, generation of a syngas stream may notprovide additional low-carbon power.

In various aspects, systems and methods are provided for producing anincreased or maximized amount of electrical power from a fixed MCFCsystem while optionally but preferably providing for consistent highcarbon capture. In some aspects, such a system can be provided bycombining the use of a conventional gas turbine as the CO₂ source forthe MCFC cathode, a low fuel utilization for production of high amountsof syngas, and a combination of separation and/or conversion systemsthat can allow for increased production of hydrogen derived from theMCFC anode exhaust. This hydrogen stream derived from the anode exhaustcan then be introduced into a second hydrogen turbine where additionalpower can be generated with reduced or minimized emissions of CO₂.Because the second turbine can be powered by the hydrogen-containingstream derived from the anode exhaust, the amount of additional CO₂generated in order to power the second turbine can be limited to, forexample, carbon oxide(s) and carbon fuel residual components in thehydrogen-containing stream. Additionally or alternatively, the hydrogenfrom the anode exhaust can be used to generate electricity in othermanners, such as by combusting the hydrogen to raise steam, which canthen be used to generate electricity. Further additionally oralternately, a portion of the hydrogen derived from the anode exhaustcan be used as an input for the first (conventional) turbine. This canbe beneficial, for example, if the carbon-containing fuel for the firstturbine has an elevated content of inerts, such as CO₂ and/or N₂.

In addition to use within a refinery, hydrogen can more generally beuseful for a wide variety of products and processes, as it produces onlywater vapor on combustion. However, most conventional approaches tomaking hydrogen can require large emissions of carbon. For example,production of hydrogen from steam reforming of methane can produce CO₂(from the carbon in the methane) and waste heat. Production of hydrogenfrom electrolysis can require electricity, which is typically generatedfor the electrical grid based on combustion of a mixture of fossilfuels. These production systems can all typically result in effluentexhausts comprising CO₂.

Applications such as fuel cell vehicles can require low-temperature fuelcells which utilize high purity hydrogen. While the vehicle does notproduce much carbon emissions, the production of the hydrogen for thevehicle can be inefficient, not easily adapted to smaller-scale, and canproduce significant carbon emissions.

In some additional or alternative aspects, the systems and methodsherein can facilitate separation of CO₂ efficiently from the process asan integral part of the separation and hydrogen purification steps. TheCO₂ can then be captured and/or used for other useful processes. Thiscan occur at high overall system efficiency, as compared to conventionalmeans of producing net hydrogen production/export, especially at smallscale and under variable load.

The use of a MCFC system for hydrogen production for use in subsequentprocesses that may generate electrical power and/or heat can allow forlow-emission energy production at high efficiency and with reduced orminimized carbon emissions. The MCFC system can dynamically respond tovarying needs for hydrogen by adjusting the ratio of chemical energyproduction to electrical energy production and can be suitable for useswhere loads and demands may not be constant—varying from heightenedelectrical production with little or no excess hydrogen to heightenedhydrogen production. Additionally, the integrated system can be scaledover a wider range of applications with high efficiency, as comparedwith larger scale systems such as methane steam reformers. This couldallow, for example, for co-production of hydrogen for other uses, suchas a fuel cell vehicle system, and for variable electrical power orsimply to vary electrical power output.

For example, in some operating configurations, the base gas turbine(such as a turbine powered by combustion of a carbon-containing fuel)can be run at constant high-efficiency conditions with the MCFC systemrun under variable fuel utilizations to yield different electrical andhydrogen production values, which can control the electrical output fromthe entire system. The amount of hydrogen and electricity can be varieddepending on overall demand while maintaining overall high systemefficiency. Hydrogen for export into boilers and/or other combined heatand power systems can allow for the constant production of electricity,e.g., in stand-alone generation, along with a variable amount ofcarbon-free heat via the production of hydrogen with subsequentcombustion in heater/boiler and/or similar systems. For example, aninstallation could produce primarily electricity in the summer for airconditioning systems while switching to a mix of primarily chemicalenergy in the winter for heating operations. During high electricaldemand, increased hydrogen can be sent to the hydrogen turbine formaximized electrical production. Other applications can include systemsdesigned to provide on-site hydrogen such as in laboratories and othertechnical and manufacturing facilities, where some hydrogen can beneeded along with a need for electrical energy.

In aspects involving hydrogen production and/or electrical powergeneration, the anode inlet can be fed by fresh methane, anothersuitable hydrocarbon fuel, and/or the combination of fresh fuel andrecycled CO and/or H₂ from the various processes. The anode outletstream comprising H₂ and/or CO can provide the components to producehydrogen. This is typically done through some combination of reaction,separation, and purification steps. An example can be a first stageemploying water-gas shift to shift as much as possible (nearly all) ofthe CO to H₂ by the reaction H₂O+CO=H₂+CO₂, followed by a second (andpotentially subsequent) stage(s) that can remove H₂O and/or CO₂ from theH₂, and can provide a suitable purity product. Such stages can includePSA, cryogenic separation, membranes, and/or other known separationmethods, either individually or in combination. The off-gasses fromthese steps can be recycled and/or can be used to provide heat for inletstreams. The separated CO₂ can be used as a recycle stream and/or can becaptured and optionally used for other processes. The cathode inlet canbe composed of recycled CO₂ from the overall process and/or of CO₂produced by the combustion of fresh (or recycled) fuel used to provideheat to the inlet streams. In some preferred aspects, the cathode inletcan include at least a portion of a combustion exhaust from a firstconventional combustion turbine. The cathode effluent can typically beexhausted to the atmosphere, optionally but preferably after heatrecovery to, for example, provide heat for other process streams and/orin combined cycle electrical production, though the cathode effluentcould optionally but less preferably be sent for further treatment, ifdesired.

MCFC systems integrated into carbon-free heat and power applications canbe used over a range of operating conditions comprising high (e.g., fromabout 60% to about 70%) fuel utilization with low hydrogen make to lowfuel utilizations (e.g., from about 20% to about 60%) with increasedhydrogen production. Examples of low fuel utilizations can include atleast about 20%, such as at least about 30%, and/or about 60% or less,such as about 50% or less. The exact operational range of an individualapplication can vary widely both by application and over time. Theability to adapt to this operational range can be a desirable advantage.The number of separation stages and the purity achieved can depend onthe ultimate application. Simple production of hydrogen forlow-emissions heat can be tolerant to modest impurities in the hydrogen,as even a few percent CO₂ and/or CO in emitted streams could stillresult in very low overall carbon emissions. High purificationapplications such as fuel cell vehicles and/or hydrogen for laboratoriescan require multiple steps (e.g. cryogenic separation, followed by PSA)to achieve purity specifications.

In other configurations, the MCFC can be operated under lower fuelutilizations with the excess anode outlet fuel used to provide heatand/or power. In both cases, an advantage can be that the “base load”power output of the fixed gas turbine and MCFC systems can remainapproximately constant, while a small sub-section of the overallprocess, the hydrogen turbine, can be used for variable load. Thecombination of variable fuel utilization and variable hydrogen turbinefeed can allow the overall plant to meet a large variety of needs forheat, electricity, and/or hydrogen demand, while operating the majorsubsystems of the plant at fairly consistent operating conditions.

FIG. 25 shows an example flow sheet of an integrated power generationMCFC process that can produce low CO₂ emissions power from a convenientcarbon-containing fuel, such as natural gas and/or methane. In thisscheme a natural gas fired turbine 2540 can combust oxidant (air) 2501and methane/natural gas 2502 to generate power and exhaust gas stream2503. Exhaust 2503 can be fed into a cathode of MCFC 2530. The anode ofMCFC 2530 can be fed additional fuel (methane/natural gas) 2505 andsteam 2506. Through an electrochemical reaction, the MCFC 2530 cangenerate power, can produce a CO₂ depleted cathode exhaust 2504, and canproduce an anode exhaust 2507 that contains H₂/CO₂/CO. Heat can berecovered from cathode exhaust 2504, and then cathode exhaust 2504 canbe emitted to the atmosphere and/or subject to further treatment, ifdesired. Anode exhaust 2507 can be shifted in a water gas shift reactor2560 to increase the H₂ concentration. The shift reactor effluent canundergo separations 2570 to remove water 2508, recover CO₂ 2509, andform a separated stream 2510 containing H₂. CO₂-containing stream 2509can be compressed to pipeline conditions and can then be sold for use,used for a different process, and/or sequestered. The separated stream2510 can be combined with oxidant (air) 2511 and sent to a hydrogenturbine 2550 to generate additional power. The exhaust 2512 from thehydrogen turbine 2550 can be mostly water and N₂ and can be emitted tothe atmosphere and/or subject to further treatment, if desired.

As an example, simulations were performed using a configuration similarto the system shown in FIG. 25. Comparative simulations were alsoperformed for systems where a hydrogen turbine was not included. In thecomparative simulations, fuel (comprising hydrogen) from the anodeexhaust was instead recycled to the combustion zone for the conventionalturbine. It is noted that the size of the conventional turbine was heldconstant in the simulations, so recycle of fuel from the anode exhaustresulted in a reduction in the amount of fresh natural gas delivered tothe conventional turbine.

The results from the simulations are shown in FIG. 26. The results inFIG. 26 appeared to show that, at conventional fuel utilizations, suchas a fuel utilization of ˜75%, use of a second hydrogen turbine may notbe as beneficial. At a fuel utilization of ˜75%, the results appeared toshow that using the second hydrogen turbine can reduce the overallefficiency of generation of electrical power while also reducing the netpower produced.

For a fuel utilization of about 50%, the simulation results in FIG. 26appeared to show the benefits of operating with a second hydrogenturbine. The overall efficiency of the system with the second hydrogenturbine still appeared to be lower, as the overall efficiency was about50% versus the ˜55% that was simulated for the comparative example.However, the simulations appeared to show that operating at about 50%fuel utilization resulted in a larger amount of power produced (about624 MW) than any of the comparative examples, while also appearing tohave lower emissions of CO₂ per MWhr (about 144 lbs/MWhr) relative toany of the comparative examples. The simulations at a fuel utilizationof about 30% appeared to show even greater benefits of producing largehydrogen volumes by operating at lower fuel utilization. The simulationsappeared to show significantly increased power production (about 790 MW)while also significantly reducing the amount of CO₂ emissions (about 113lbs/MWhr). The combination of increased power and reduced CO₂ emissionsappeared to be achieved in the simulations in part due to the increasedamount of CO₂ captured (about 1.92 Mtons/yr at about 50% fuelutilization, about 2.56 Mtons/year at about 30% fuel utilization). As aresult, the simulations appeared to show that use of a hydrogen turbine,in combination with a fuel utilization of about 60% or less, such asabout 50% or less, can provide unexpectedly low CO₂ emissions per unitof energy generated while providing increased electrical energyproduction.

Additional Fuel Cell Operation Strategies

As an addition, complement, and/or alternative to the fuel celloperating strategies described herein, a molten carbonate fuel cell canbe operated so that the amount of reforming can be selected relative tothe amount of oxidation in order to achieve a desired thermal ratio forthe fuel cell. As used herein, the “thermal ratio” is defined as theheat produced by exothermic reactions in a fuel cell assembly divided bythe endothermic heat demand of reforming reactions occurring within thefuel cell assembly. Expressed mathematically, the thermal ratio(TH)=Q_(EX)/Q_(EN), where Q_(EX) is the sum of heat produced byexothermic reactions and Q_(EN) is the sum of heat consumed by theendothermic reactions occurring within the fuel cell. Note that the heatproduced by the exothermic reactions corresponds to any heat due toreforming reactions, water gas shift reactions, and the electrochemicalreactions in the cell. The heat generated by the electrochemicalreactions can be calculated based on the ideal electrochemical potentialof the fuel cell reaction across the electrolyte minus the actual outputvoltage of the fuel cell. For example, the ideal electrochemicalpotential of the reaction in a MCFC is believed to be about 1.04V basedon the net reaction that occurs in the cell. During operation of theMCFC, the cell will typically have an output voltage less than 1.04 Vdue to various losses. For example, a common output/operating voltagecan be about 0.7 V. The heat generated is equal to the electrochemicalpotential of the cell (i.e. ˜1.04V) minus the operating voltage. Forexample, the heat produced by the electrochemical reactions in the cellis ˜0.34 V when the output voltage of ˜0.7V. Thus, in this scenario, theelectrochemical reactions would produce ˜0.7 V of electricity and ˜0.34V of heat energy. In such an example, the ˜0.7 V of electrical energy isnot included as part of Q_(EX). In other words, heat energy is notelectrical energy.

In various aspects, a thermal ratio can be determined for any convenientfuel cell structure, such as a fuel cell stack, an individual fuel cellwithin a fuel cell stack, a fuel cell stack with an integrated reformingstage, a fuel cell stack with an integrated endothermic reaction stage,or a combination thereof. The thermal ratio may also be calculated fordifferent units within a fuel cell stack, such as an assembly of fuelcells or fuel cell stacks. For example, the thermal ratio may becalculated for a single anode within a single fuel cell, an anodesection within a fuel cell stack, or an anode section within a fuel cellstack along with integrated reforming stages and/or integratedendothermic reaction stage elements in sufficiently close proximity tothe anode section to be integrated from a heat integration standpoint.As used herein, “an anode section” comprises anodes within a fuel cellstack that share a common inlet or outlet manifold.

In various aspects of the invention, the operation of the fuel cells canbe characterized based on a thermal ratio. Where fuel cells are operatedto have a desired thermal ratio, a molten carbonate fuel cell can beoperated to have a thermal ratio of about 1.5 or less, for example about1.3 or less, or about 1.15 or less, or about 1.0 or less, or about 0.95or less, or about 0.90 or less, or about 0.85 or less, or about 0.80 orless, or about 0.75 or less. Additionally or alternately, the thermalratio can be at least about 0.25, or at least about 0.35, or at leastabout 0.45, or at least about 0.50. Additionally or alternately, in someaspects the fuel cell can be operated to have a temperature rise betweenanode input and anode output of about 40° C. or less, such as about 20°C. or less, or about 10° C. or less. Further additionally oralternately, the fuel cell can be operated to have an anode outlettemperature that is from about 10° C. lower to about 10° C. higher thanthe temperature of the anode inlet. Still further additionally oralternately, the fuel cell can be operated to have an anode inlettemperature that is greater than the anode outlet temperature, such asat least about 5° C. greater, or at least about 10° C. greater, or atleast about 20° C. greater, or at least about 25° C. greater. Yet stillfurther additionally or alternately, the fuel cell can be operated tohave an anode inlet temperature that is greater than the anode outlettemperature by about 100° C. or less, such as by about 80° C. or less,or about 60° C. or less, or about 50° C. or less, or about 40° C. orless, or about 30° C. or less, or about 20° C. or less.

As an addition, complement, and/or alternative to the fuel celloperating strategies described herein, a molten carbonate fuel cell(such as a fuel cell assembly) can be operated with increased productionof syngas (or hydrogen) while also reducing or minimizing the amount ofCO₂ exiting the fuel cell in the cathode exhaust stream. Syngas can be avaluable input for a variety of processes. In addition to having fuelvalue, syngas can be used as a raw material for forming other highervalue products, such as by using syngas as an input for Fischer-Tropschsynthesis and/or methanol synthesis processes. One option for makingsyngas can be to reform a hydrocarbon or hydrocarbon-like fuel, such asmethane or natural gas. For many types of industrial processes, a syngashaving a ratio of H₂ to CO of close to 2:1 (or even lower) can often bedesirable. A water gas shift reaction can be used to reduce the H₂ to COratio in a syngas if additional CO₂ is available, such as is produced inthe anodes.

One way of characterizing the overall benefit provided by integratingsyngas generation with use of molten carbonate fuel cells can be basedon a ratio of the net amount of syngas that exits the fuel cells in theanode exhaust relative to the amount of CO₂ that exits the fuel cells inthe cathode exhaust. This characterization measures the effectiveness ofproducing power with low emissions and high efficiency (both electricaland chemical). In this description, the net amount of syngas in an anodeexhaust is defined as the combined number of moles of H₂ and number ofmoles of CO present in the anode exhaust, offset by the amount of H₂ andCO present in the anode inlet. Because the ratio is based on the netamount of syngas in the anode exhaust, simply passing excess H₂ into theanode does not change the value of the ratio. However, H₂ and/or COgenerated due to reforming in the anode and/or in an internal reformingstage associated with the anode can lead to higher values of the ratio.Hydrogen oxidized in the anode can lower the ratio. It is noted that thewater gas shift reaction can exchange H₂ for CO, so the combined molesof H₂ and CO represents the total potential syngas in the anode exhaust,regardless of the eventual desired ratio of H₂ to CO in a syngas. Thesyngas content of the anode exhaust (H₂+CO) can then be compared withthe CO₂ content of the cathode exhaust. This can provide a type ofefficiency value that can also account for the amount of carbon capture.This can equivalently be expressed as an equation asRatio of net syngas in anode exhaust to cathode CO₂=net moles of(H₂+CO)_(ANODE)/moles of (CO₂)_(CATHODE)

In various aspects, the ratio of net moles of syngas in the anodeexhaust to the moles of CO₂ in the cathode exhaust can be at least about2.0, such as at least about 3.0, or at least about 4.0, or at leastabout 5.0. In some aspects, the ratio of net syngas in the anode exhaustto the amount of CO₂ in the cathode exhaust can be still higher, such asat least about 10.0, or at least about 15.0, or at least about 20.0.Ratio values of about 40.0 or less, such as about 30.0 or less, or about20.0 or less, can additionally or alternately be achieved. In aspectswhere the amount of CO₂ at the cathode inlet is about 6.0 volume % orless, such as about 5.0 volume % or less, ratio values of at least about1.5 may be sufficient/realistic. Such molar ratio values of net syngasin the anode exhaust to the amount of CO₂ in the cathode exhaust can begreater than the values for conventionally operated fuel cells.

As an addition, complement, and/or alternative to the fuel celloperating strategies described herein, a molten carbonate fuel cell(such as a fuel cell assembly) can be operated at a reduced fuelutilization value, such as a fuel utilization of about 50% or less,while also having a high CO₂ utilization value, such as at least about60%.

In this type of configuration, the molten carbonate fuel cell can beeffective for carbon capture, as the CO₂ utilization can advantageouslybe sufficiently high. Rather than attempting to maximize electricalefficiency, in this type of configuration the total efficiency of thefuel cell can be improved or increased based on the combined electricaland chemical efficiency. The chemical efficiency can be based onwithdrawal of a hydrogen and/or syngas stream from the anode exhaust asan output for use in other processes. Even though the electricalefficiency may be reduced relative to some conventional configurations,making use of the chemical energy output in the anode exhaust can allowfor a desirable total efficiency for the fuel cell.

In various aspects, the fuel utilization in the fuel cell anode can beabout 50% or less, such as about 40% or less, or about 30% or less, orabout 25% or less, or about 20% or less. In various aspects, in order togenerate at least some electric power, the fuel utilization in the fuelcell can be at least about 5%, such as at least about 10%, or at leastabout 15%, or at least about 20%, or at least about 25%, or at leastabout 30%. Additionally or alternatively, the CO₂ utilization can be atleast about 60%, such as at least about 65%, or at least about 70%, orat least about 75%.

As an addition, complement, and/or alternative to the fuel celloperating strategies described herein, a molten carbonate fuel cell canbe operated at conditions that increase or maximize syngas production,possibly at the detriment of electricity production and electricalefficiency. Instead of selecting the operating conditions of a fuel cellto improve or maximize the electrical efficiency of the fuel cell,operating conditions, possibly including an amount of reformable fuelpassed into the anode, can be established to increase the chemicalenergy output of the fuel cell. These operating conditions can result ina lower electrical efficiency of the fuel cell. Despite the reducedelectrical efficiency, optionally, but preferably, the operatingconditions can lead to an increase in the total efficiency of the fuelcell, which is based on the combined electrical efficiency and chemicalefficiency of the fuel cell. By increasing the ratio of reformable fuelintroduced into the anode to the fuel that is actually electrochemicallyoxidized at the anode, the chemical energy content in the anode outputcan be increased.

In some aspects, the reformable hydrogen content of reformable fuel inthe input stream delivered to the anode and/or to a reforming stageassociated with the anode can be at least about 50% greater than the netamount of hydrogen reacted at the anode, such as at least about 75%greater or at least about 100% greater. Additionally or alternately, thereformable hydrogen content of fuel in the input stream delivered to theanode and/or to a reforming stage associated with the anode can be atleast about 50% greater than the net amount of hydrogen reacted at theanode, such as at least about 75% greater or at least about 100%greater. In various aspects, a ratio of the reformable hydrogen contentof the reformable fuel in the fuel stream relative to an amount ofhydrogen reacted in the anode can be at least about 1.5:1, or at leastabout 2.0:1, or at least about 2.5:1, or at least about 3.0:1.Additionally or alternately, the ratio of reformable hydrogen content ofthe reformable fuel in the fuel stream relative to the amount ofhydrogen reacted in the anode can be about 20:1 or less, such as about15:1 or less or about 10:1 or less. In one aspect, it is contemplatedthat less than 100% of the reformable hydrogen content in the anodeinlet stream can be converted to hydrogen. For example, at least about80% of the reformable hydrogen content in an anode inlet stream can beconverted to hydrogen in the anode and/or in an associated reformingstage(s), such as at least about 85%, or at least about 90%.Additionally or alternately, the amount of reformable fuel delivered tothe anode can be characterized based on the Lower Heating Value (LHV) ofthe reformable fuel relative to the LHV of the hydrogen oxidized in theanode. This can be referred to as a reformable fuel surplus ratio. Invarious aspects, the reformable fuel surplus ratio can be at least about2.0, such as at least about 2.5, or at least about 3.0, or at leastabout 4.0. Additionally or alternately, the reformable fuel surplusratio can be about 25.0 or less, such as about 20.0 or less, or about15.0 or less, or about 10.0 or less.

As an addition, complement, and/or alternative to the fuel celloperating strategies described herein, a molten carbonate fuel cell(such as a fuel cell assembly) can also be operated at conditions thatcan improve or optimize the combined electrical efficiency and chemicalefficiency of the fuel cell. Instead of selecting conventionalconditions for maximizing the electrical efficiency of a fuel cell, theoperating conditions can allow for output of excess synthesis gas and/orhydrogen in the anode exhaust of the fuel cell. The synthesis gas and/orhydrogen can then be used in a variety of applications, includingchemical synthesis processes and collection of hydrogen for use as a“clean” fuel. In aspects of the invention, electrical efficiency can bereduced to achieve a high overall efficiency, which includes a chemicalefficiency based on the chemical energy value of syngas and/or hydrogenproduced relative to the energy value of the fuel input for the fuelcell.

In some aspects, the operation of the fuel cells can be characterizedbased on electrical efficiency. Where fuel cells are operated to have alow electrical efficiency (EE), a molten carbonate fuel cell can beoperated to have an electrical efficiency of about 40% or less, forexample, about 35% EE or less, about 30% EE or less, about 25% EE orless, or about 20% EE or less, about 15% EE or less, or about 10% EE orless. Additionally or alternately, the EE can be at least about 5%, orat least about 10%, or at least about 15%, or at least about 20%.Further additionally or alternately, the operation of the fuel cells canbe characterized based on total fuel cell efficiency (TFCE), such as acombined electrical efficiency and chemical efficiency of the fuelcell(s). Where fuel cells are operated to have a high total fuel cellefficiency, a molten carbonate fuel cell can be operated to have a TFCE(and/or combined electrical efficiency and chemical efficiency) of about55% or more, for example, about 60% or more, or about 65% or more, orabout 70% or more, or about 75% or more, or about 80% or more, or about85% or more. It is noted that for a total fuel cell efficiency and/orcombined electrical efficiency and chemical efficiency, any additionalelectricity generated from use of excess heat generated by the fuel cellcan be excluded from the efficiency calculation.

In various aspects of the invention, the operation of the fuel cells canbe characterized based on a desired electrical efficiency of about 40%or less and a desired total fuel cell efficiency of about 55% or more.Where fuel cells are operated to have a desired electrical efficiencyand a desired total fuel cell efficiency, a molten carbonate fuel cellcan be operated to have an electrical efficiency of about 40% or lesswith a TFCE of about 55% or more, for example, about 35% EE or less withabout a TFCE of 60% or more, about 30% EE or less with about a TFCE ofabout 65% or more, about 25% EE or less with about a 70% TFCE or more,or about 20% EE or less with about a TFCE of 75% or more, about 15% EEor less with about a TFCE of 80% or more, or about 10% EE or less withabout a TFCE of about 85% or more.

As an addition, complement, and/or alternative to the fuel celloperating strategies described herein, a molten carbonate fuel cell(such as a fuel cell assembly) can be operated at conditions that canprovide increased power density. The power density of a fuel cellcorresponds to the actual operating voltage V_(A) multiplied by thecurrent density I. For a molten carbonate fuel cell operating at avoltage V_(A), the fuel cell also can tend to generate waste heat, thewaste heat defined as (V₀−V_(A))*I based on the differential betweenV_(A) and the ideal voltage V₀ for a fuel cell providing current densityI. A portion of this waste heat can be consumed by reforming of areformable fuel within the anode of the fuel cell. The remaining portionof this waste heat can be absorbed by the surrounding fuel cellstructures and gas flows, resulting in a temperature differential acrossthe fuel cell. Under conventional operating conditions, the powerdensity of a fuel cell can be limited based on the amount of waste heatthat the fuel cell can tolerate without compromising the integrity ofthe fuel cell.

In various aspects, the amount of waste heat that a fuel cell cantolerate can be increased by performing an effective amount of anendothermic reaction within the fuel cell. One example of an endothermicreaction includes steam reforming of a reformable fuel within a fuelcell anode and/or in an associated reforming stage, such as anintegrated reforming stage in a fuel cell stack. By providing additionalreformable fuel to the anode of the fuel cell (or to anintegrated/associated reforming stage), additional reforming can beperformed so that additional waste heat can be consumed. This can reducethe amount of temperature differential across the fuel cell, thusallowing the fuel cell to operate under an operating condition with anincreased amount of waste heat. The loss of electrical efficiency can beoffset by the creation of an additional product stream, such as syngasand/or H₂, that can be used for various purposes including additionalelectricity generation further expanding the power range of the system.

In various aspects, the amount of waste heat generated by a fuel cell,(V₀−V_(A))*I as defined above, can be at least about 30 mW/cm², such asat least about 40 mW/cm², or at least about 50 mW/cm², or at least about60 mW/cm², or at least about 70 mW/cm², or at least about 80 mW/cm², orat least about 100 mW/cm², or at least about 120 mW/cm², or at leastabout 140 mW/cm², or at least about 160 mW/cm², or at least about 180mW/cm². Additionally or alternately, the amount of waste heat generatedby a fuel cell can be less than about 250 mW/cm², such as less thanabout 200 mW/cm², or less than about 180 mW/cm², or less than about 165mW/cm², or less than about 150 mW/cm².

Although the amount of waste heat being generated can be relativelyhigh, such waste heat may not necessarily represent operating a fuelcell with poor efficiency. Instead, the waste heat can be generated dueto operating a fuel cell at an increased power density. Part ofimproving the power density of a fuel cell can include operating thefuel cell at a sufficiently high current density. In various aspects,the current density generated by the fuel cell can be at least about 150mA/cm², such as at least about 160 mA/cm², or at least about 170 mA/cm²,or at least about 180 mA/cm², or at least about 190 mA/cm², or at leastabout 200 mA/cm², or at least about 225 mA/cm², or at least about 250mA/cm². Additionally or alternately, the current density generated bythe fuel cell can be about 500 mA/cm² or less, such as 450 mA/cm², orless, or 400 mA/cm², or less or 350 mA/cm², or less or 300 mA/cm² orless.

In various aspects, to allow a fuel cell to be operated with increasedpower generation and increased generation of waste heat, an effectiveamount of an endothermic reaction (such as a reforming reaction) can beperformed. Alternatively, other endothermic reactions unrelated to anodeoperations can be used to utilize the waste heat by interspersing“plates” or stages into the fuel cell array that are in thermalcommunication but not fluid communication. The effective amount of theendothermic reaction can be performed in an associated reforming stage,an integrated reforming stage, an integrated stack element forperforming an endothermic reaction, or a combination thereof. Theeffective amount of the endothermic reaction can correspond to an amountsufficient to reduce the temperature rise from the fuel cell inlet tothe fuel cell outlet to about 100° C. or less, such as about 90° C. orless, or about 80° C. or less, or about 70° C. or less, or about 60° C.or less, or about 50° C. or less, or about 40° C. or less, or about 30°C. or less. Additionally or alternately, the effective amount of theendothermic reaction can correspond to an amount sufficient to cause atemperature decrease from the fuel cell inlet to the fuel cell outlet ofabout 100° C. or less, such as about 90° C. or less, or about 80° C. orless, or about 70° C. or less, or about 60° C. or less, or about 50° C.or less, or about 40° C. or less, or about 30° C. or less, or about 20°C. or less, or about 10° C. or less. A temperature decrease from thefuel cell inlet to the fuel cell outlet can occur when the effectiveamount of the endothermic reaction exceeds the waste heat generated.Additionally or alternately, this can correspond to having theendothermic reaction(s) (such as a combination of reforming and anotherendothermic reaction) consume at least about 40% of the waste heatgenerated by the fuel cell, such as consuming at least about 50% of thewaste heat, or at least about 60% of the waste heat, or at least about75% of the waste heat. Further additionally or alternately, theendothermic reaction(s) can consume about 95% of the waste heat or less,such as about 90% of the waste heat or less, or about 85% of the wasteheat or less.

As an addition, complement, and/or alternative to the fuel celloperating strategies described herein, a molten carbonate fuel cell(such as a fuel cell assembly) can be operated at conditionscorresponding to a decreased operating voltage and a low fuelutilization. In various aspects, the fuel cell can be operated at avoltage V_(A) of less than about 0.7 Volts, for example less than about0.68 V, less than about 0.67 V, less than about 0.66 V, or about 0.65 Vor less. Additionally or alternatively, the fuel cell can be operated ata voltage V_(A) of at least about 0.60, for example at least about 0.61,at least about 0.62, or at least about 0.63. In so doing, energy thatwould otherwise leave the fuel cell as electrical energy at high voltagecan remain within the cell as heat as the voltage is lowered. Thisadditional heat can allow for increased endothermic reactions to occur,for example increasing the CH₄ conversion to syngas.

Definitions

Syngas: In this description, syngas is defined as mixture of H₂ and COin any ratio. Optionally, H₂O and/or CO₂ may be present in the syngas.Optionally, inert compounds (such as nitrogen) and residual reformablefuel compounds may be present in the syngas. If components other than H₂and CO are present in the syngas, the combined volume percentage of H₂and CO in the syngas can be at least 25 vol % relative to the totalvolume of the syngas, such as at least 40 vol %, or at least 50 vol %,or at least 60 vol %. Additionally or alternately, the combined volumepercentage of H₂ and CO in the syngas can be 100 vol % or less, such as95 vol % or less or 90 vol % or less.

Reformable fuel: A reformable fuel is defined as a fuel that containscarbon-hydrogen bonds that can be reformed to generate H₂. Hydrocarbonsare examples of reformable fuels, as are other hydrocarbonaceouscompounds such as alcohols. Although CO and H₂O can participate in awater gas shift reaction to form hydrogen, CO is not considered areformable fuel under this definition.

Reformable hydrogen content: The reformable hydrogen content of a fuelis defined as the number of H₂ molecules that can be derived from a fuelby reforming the fuel and then driving the water gas shift reaction tocompletion to maximize H₂ production. It is noted that H₂ by definitionhas a reformable hydrogen content of 1, although H₂ itself is notdefined as a reformable fuel herein. Similarly, CO has a reformablehydrogen content of 1. Although CO is not strictly reformable, drivingthe water gas shift reaction to completion will result in exchange of aCO for an H₂. As examples of reformable hydrogen content for reformablefuels, the reformable hydrogen content of methane is 4H₂ molecules whilethe reformable hydrogen content of ethane is 7H₂ molecules. Moregenerally, if a fuel has the composition CxHyOz, then the reformablehydrogen content of the fuel at 100% reforming and water-gas shift isn(H₂ max reforming)=2x+y/2−z. Based on this definition, fuel utilizationwithin a cell can then be expressed as n(H₂ ox)/n(H₂ max reforming). Ofcourse, the reformable hydrogen content of a mixture of components canbe determined based on the reformable hydrogen content of the individualcomponents. The reformable hydrogen content of compounds that containother heteroatoms, such as oxygen, sulfur or nitrogen, can also becalculated in a similar manner.

Oxidation Reaction: In this discussion, the oxidation reaction withinthe anode of a fuel cell is defined as the reaction corresponding tooxidation of H₂ by reaction with CO₃ ²⁻ to form H₂O and CO₂. It is notedthat the reforming reaction within the anode, where a compoundcontaining a carbon-hydrogen bond is converted into H₂ and CO or CO₂, isexcluded from this definition of the oxidation reaction in the anode.The water-gas shift reaction is similarly outside of this definition ofthe oxidation reaction. It is further noted that references to acombustion reaction are defined as references to reactions where H₂ or acompound containing carbon-hydrogen bond(s) are reacted with O₂ to formH₂O and carbon oxides in a non-electrochemical burner, such as thecombustion zone of a combustion-powered generator.

Aspects of the invention can adjust anode fuel parameters to achieve adesired operating range for the fuel cell. Anode fuel parameters can becharacterized directly, and/or in relation to other fuel cell processesin the form of one or more ratios. For example, the anode fuelparameters can be controlled to achieve one or more ratios including afuel utilization, a fuel cell heating value utilization, a fuel surplusratio, a reformable fuel surplus ratio, a reformable hydrogen contentfuel ratio, and combinations thereof.

Fuel utilization: Fuel utilization is an option for characterizingoperation of the anode based on the amount of oxidized fuel relative tothe reformable hydrogen content of an input stream can be used to definea fuel utilization for a fuel cell. In this discussion, “fuelutilization” is defined as the ratio of the amount of hydrogen oxidizedin the anode for production of electricity (as described above) versusthe reformable hydrogen content of the anode input (including anyassociated reforming stages).

Reformable hydrogen content has been defined above as the number of H₂molecules that can be derived from a fuel by reforming the fuel and thendriving the water gas shift reaction to completion to maximize H₂production. For example, each methane introduced into an anode andexposed to steam reforming conditions results in generation of theequivalent of 4H₂ molecules at max production. (Depending on thereforming and/or anode conditions, the reforming product can correspondto a non-water gas shifted product, where one or more of the H₂molecules is present instead in the form of a CO molecule.) Thus,methane is defined as having a reformable hydrogen content of 4H₂molecules. As another example, under this definition ethane has areformable hydrogen content of 7H₂ molecules.

The utilization of fuel in the anode can also be characterized bydefining a heating value utilization based on a ratio of the LowerHeating Value of hydrogen oxidized in the anode due to the fuel cellanode reaction relative to the Lower Heating Value of all fuel deliveredto the anode and/or a reforming stage associated with the anode. The“fuel cell heating value utilization” as used herein can be computedusing the flow rates and Lower Heating Value (LHV) of the fuelcomponents entering and leaving the fuel cell anode. As such, fuel cellheating value utilization can be computed as(LHV(anode_in)−LHV(anode_out))/LHV(anode_in), where LHV(anode_in) andLHV(anode_out) refer to the LHV of the fuel components (such as H₂, CH₄,and/or CO) in the anode inlet and outlet streams or flows, respectively.In this definition, the LHV of a stream or flow may be computed as a sumof values for each fuel component in the input and/or output stream. Thecontribution of each fuel component to the sum can correspond to thefuel component's flow rate (e.g., mol/hr) multiplied by the fuelcomponent's LHV (e.g., joules/mol).

Lower Heating Value: The lower heating value is defined as the enthalpyof combustion of a fuel component to vapor phase, fully oxidizedproducts (i.e., vapor phase CO₂ and H₂O product). For example, any CO₂present in an anode input stream does not contribute to the fuel contentof the anode input, since CO₂ is already fully oxidized. For thisdefinition, the amount of oxidation occurring in the anode due to theanode fuel cell reaction is defined as oxidation of H₂ in the anode aspart of the electrochemical reaction in the anode, as defined above.

It is noted that, for the special case where the only fuel in the anodeinput flow is H₂, the only reaction involving a fuel component that cantake place in the anode represents the conversion of H₂ into H₂O. Inthis special case, the fuel utilization simplifies to (H₂-rate-in minusH₂-rate-out)/H₂-rate-in. In such a case, H₂ would be the only fuelcomponent, and so the H₂ LHV would cancel out of the equation. In themore general case, the anode feed may contain, for example, CH₄, H₂, andCO in various amounts. Because these species can typically be present indifferent amounts in the anode outlet, the summation as described abovecan be needed to determine the fuel utilization.

Alternatively or in addition to fuel utilization, the utilization forother reactants in the fuel cell can be characterized. For example, theoperation of a fuel cell can additionally or alternately becharacterized with regard to “CO₂ utilization” and/or “oxidant”utilization. The values for CO₂ utilization and/or oxidant utilizationcan be specified in a similar manner.

Fuel surplus ratio: Still another way to characterize the reactions in amolten carbonate fuel cell is by defining a utilization based on a ratioof the Lower Heating Value of all fuel delivered to the anode and/or areforming stage associated with the anode relative to the Lower HeatingValue of hydrogen oxidized in the anode due to the fuel cell anodereaction. This quantity will be referred to as a fuel surplus ratio. Assuch the fuel surplus ratio can be computed as (LHV(anode_in)/(LHV(anode_in)−LHV(anode_out)) where LHV(anode_in) andLHV(anode_out) refer to the LHV of the fuel components (such as H₂, CH₄,and/or CO) in the anode inlet and outlet streams or flows, respectively.In various aspects of the invention, a molten carbonate fuel cell can beoperated to have a fuel surplus ratio of at least about 1.0, such as atleast about 1.5, or at least about 2.0, or at least about 2.5, or atleast about 3.0, or at least about 4.0. Additionally or alternately, thefuel surplus ratio can be about 25.0 or less.

It is noted that not all of the reformable fuel in the input stream forthe anode may be reformed. Preferably, at least about 90% of thereformable fuel in the input stream to the anode (and/or into anassociated reforming stage) can be reformed prior to exiting the anode,such as at least about 95% or at least about 98%. In some alternativeaspects, the amount of reformable fuel that is reformed can be fromabout 75% to about 90%, such as at least about 80%.

The above definition for fuel surplus ratio provides a method forcharacterizing the amount of reforming occurring within the anode and/orreforming stage(s) associated with a fuel cell relative to the amount offuel consumed in the fuel cell anode for generation of electric power.

Optionally, the fuel surplus ratio can be modified to account forsituations where fuel is recycled from the anode output to the anodeinput. When fuel (such as H₂, CO, and/or unreformed or partiallyreformed hydrocarbons) is recycled from anode output to anode input,such recycled fuel components do not represent a surplus amount ofreformable or reformed fuel that can be used for other purposes.Instead, such recycled fuel components merely indicate a desire toreduce fuel utilization in a fuel cell.

Reformable fuel surplus ratio: Calculating a reformable fuel surplusratio is one option to account for such recycled fuel components is tonarrow the definition of surplus fuel, so that only the LHV ofreformable fuels is included in the input stream to the anode. As usedherein the “reformable fuel surplus ratio” is defined as the LowerHeating Value of reformable fuel delivered to the anode and/or areforming stage associated with the anode relative to the Lower HeatingValue of hydrogen oxidized in the anode due to the fuel cell anodereaction. Under the definition for reformable fuel surplus ratio, theLHV of any H₂ or CO in the anode input is excluded. Such an LHV ofreformable fuel can still be measured by characterizing the actualcomposition entering a fuel cell anode, so no distinction betweenrecycled components and fresh components needs to be made. Although somenon-reformed or partially reformed fuel may also be recycled, in mostaspects the majority of the fuel recycled to the anode can correspond toreformed products such as H₂ or CO. Expressed mathematically, thereformable fuel surplus ratio (R_(RFS))=LHV_(RF)/LHV_(OH), whereLHV_(RF) is the Lower Heating Value (LHV) of the reformable fuel andLHV_(OH) is the Lower Heating Value (LHV) of the hydrogen oxidized inthe anode. The LHV of the hydrogen oxidized in the anode may becalculated by subtracting the LHV of the anode outlet stream from theLHV of the anode inlet stream (e.g., LHV(anode_in)−LHV(anode_out)). Invarious aspects of the invention, a molten carbonate fuel cell can beoperated to have a reformable fuel surplus ratio of at least about 0.25,such as at least about 0.5, or at least about 1.0, or at least about1.5, or at least about 2.0, or at least about 2.5, or at least about3.0, or at least about 4.0. Additionally or alternately, the reformablefuel surplus ratio can be about 25.0 or less. It is noted that thisnarrower definition based on the amount of reformable fuel delivered tothe anode relative to the amount of oxidation in the anode candistinguish between two types of fuel cell operation methods that havelow fuel utilization. Some fuel cells achieve low fuel utilization byrecycling a substantial portion of the anode output back to the anodeinput. This recycle can allow any hydrogen in the anode input to be usedagain as an input to the anode. This can reduce the amount of reforming,as even though the fuel utilization is low for a single pass through thefuel cell, at least a portion of the unused fuel is recycled for use ina later pass. Thus, fuel cells with a wide variety of fuel utilizationvalues may have the same ratio of reformable fuel delivered to the anodereforming stage(s) versus hydrogen oxidized in the anode reaction. Inorder to change the ratio of reformable fuel delivered to the anodereforming stages relative to the amount of oxidation in the anode,either an anode feed with a native content of non-reformable fuel needsto be identified, or unused fuel in the anode output needs to bewithdrawn for other uses, or both.

Reformable hydrogen surplus ratio: Still another option forcharacterizing the operation of a fuel cell is based on a “reformablehydrogen surplus ratio.” The reformable fuel surplus ratio defined aboveis defined based on the lower heating value of reformable fuelcomponents. The reformable hydrogen surplus ratio is defined as thereformable hydrogen content of reformable fuel delivered to the anodeand/or a reforming stage associated with the anode relative to thehydrogen reacted in the anode due to the fuel cell anode reaction. Assuch, the “reformable hydrogen surplus ratio” can be computed as(RFC(reformable_anode_in)/(RFC(reformable_anode_in)−RFC(anode_out)),where RFC(reformable_anode_in) refers to the reformable hydrogen contentof reformable fuels in the anode inlet streams or flows, while RFC(anode_out) refers to the reformable hydrogen content of the fuelcomponents (such as H₂, CH₄, and/or CO) in the anode inlet and outletstreams or flows. The RFC can be expressed in moles/s, moles/hr, orsimilar. An example of a method for operating a fuel cell with a largeratio of reformable fuel delivered to the anode reforming stage(s)versus amount of oxidation in the anode can be a method where excessreforming is performed in order to balance the generation andconsumption of heat in the fuel cell. Reforming a reformable fuel toform H₂ and CO is an endothermic process. This endothermic reaction canbe countered by the generation of electrical current in the fuel cell,which can also produce excess heat corresponding (roughly) to thedifference between the amount of heat generated by the anode oxidationreaction and the carbonate formation reaction and the energy that exitsthe fuel cell in the form of electric current. The excess heat per moleof hydrogen involved in the anode oxidation reaction/carbonate formationreaction can be greater than the heat absorbed to generate a mole ofhydrogen by reforming. As a result, a fuel cell operated underconventional conditions can exhibit a temperature increase from inlet tooutlet. Instead of this type of conventional operation, the amount offuel reformed in the reforming stages associated with the anode can beincreased. For example, additional fuel can be reformed so that the heatgenerated by the exothermic fuel cell reactions can be (roughly)balanced by the heat consumed in reforming, or even the heat consumed byreforming can be beyond the excess heat generated by the fuel oxidation,resulting in a temperature drop across the fuel cell. This can result ina substantial excess of hydrogen relative to the amount needed forelectrical power generation. As one example, a feed to the anode inletof a fuel cell or an associated reforming stage can be substantiallycomposed of reformable fuel, such as a substantially pure methane feed.During conventional operation for electric power generation using such afuel, a molten carbonate fuel cell can be operated with a fuelutilization of about 75%. This means that about 75% (or ¾) of the fuelcontent delivered to the anode is used to form hydrogen that is thenreacted in the anode with carbonate ions to form H₂O and CO₂. Inconventional operation, the remaining about 25% of the fuel content canbe reformed to H₂ within the fuel cell (or can pass through the fuelcell unreacted for any CO or H₂ in the fuel), and then combusted outsideof the fuel cell to form H₂O and CO₂ to provide heat for the cathodeinlet to the fuel cell. The reformable hydrogen surplus ratio in thissituation can be 4/(4−1)=4/3.

Electrical efficiency: As used herein, the term “electrical efficiency”(“EE”) is defined as the electrochemical power produced by the fuel celldivided by the rate of Lower Heating Value (“LHV”) of fuel input to thefuel cell. The fuel inputs to the fuel cell includes both fuel deliveredto the anode as well as any fuel used to maintain the temperature of thefuel cell, such as fuel delivered to a burner associated with a fuelcell. In this description, the power produced by the fuel may bedescribed in terms of LHV(el) fuel rate.

Electrochemical power: As used herein, the term “electrochemical power”or LHV(el) is the power generated by the circuit connecting the cathodeto the anode in the fuel cell and the transfer of carbonate ions acrossthe fuel cell's electrolyte. Electrochemical power excludes powerproduced or consumed by equipment upstream or downstream from the fuelcell. For example, electricity produced from heat in a fuel cell exhauststream is not considered part of the electrochemical power. Similarly,power generated by a gas turbine or other equipment upstream of the fuelcell is not part of the electrochemical power generated. The“electrochemical power” does not take electrical power consumed duringoperation of the fuel cell into account, or any loss incurred byconversion of the direct current to alternating current. In other words,electrical power used to supply the fuel cell operation or otherwiseoperate the fuel cell is not subtracted from the direct current powerproduced by the fuel cell. As used herein, the power density is thecurrent density multiplied by voltage. As used herein, the total fuelcell power is the power density multiplied by the fuel cell area.

Fuel inputs: As used herein, the term “anode fuel input,” designated asLHV(anode_in), is the amount of fuel within the anode inlet stream. Theterm “fuel input”, designated as LHV(in), is the total amount of fueldelivered to the fuel cell, including both the amount of fuel within theanode inlet stream and the amount of fuel used to maintain thetemperature of the fuel cell. The fuel may include both reformable andnonreformable fuels, based on the definition of a reformable fuelprovided herein. Fuel input is not the same as fuel utilization.

Total fuel cell efficiency: As used herein, the term “total fuel cellefficiency” (“TFCE”) is defined as: the electrochemical power generatedby the fuel cell, plus the rate of LHV of syngas produced by the fuelcell, divided by the rate of LHV of fuel input to the anode. In otherwords, TFCE=(LHV(el)+LHV(sg net))/LHV(anode_in), where LHV(anode_in)refers to rate at which the LHV of the fuel components (such as H₂, CH₄,and/or CO) delivered to the anode and LHV(sg net) refers to a rate atwhich syngas (H₂, CO) is produced in the anode, which is the differencebetween syngas input to the anode and syngas output from the anode.LHV(el) describes the electrochemical power generation of the fuel cell.The total fuel cell efficiency excludes heat generated by the fuel cellthat is put to beneficial use outside of the fuel cell. In operation,heat generated by the fuel cell may be put to beneficial use bydownstream equipment. For example, the heat may be used to generateadditional electricity or to heat water. These uses, when they occurapart from the fuel cell, are not part of the total fuel cellefficiency, as the term is used in this application. The total fuel cellefficiency is for the fuel cell operation only, and does not includepower production, or consumption, upstream, or downstream, of the fuelcell.

Chemical efficiency: As used herein, the term “chemical efficiency”, isdefined as the lower heating value of H₂ and CO in the anode exhaust ofthe fuel cell, or LHV(sg out), divided by the fuel input, or LHV(in).

Neither the electrical efficiency nor the total system efficiency takesthe efficiency of upstream or downstream processes into consideration.For example, it may be advantageous to use turbine exhaust as a sourceof CO₂ for the fuel cell cathode. In this arrangement, the efficiency ofthe turbine is not considered as part of the electrical efficiency orthe total fuel cell efficiency calculation. Similarly, outputs from thefuel cell may be recycled as inputs to the fuel cell. A recycle loop isnot considered when calculating electrical efficiency or the total fuelcell efficiency in single pass mode.

Syngas produced: As used herein, the term “syngas produced” is thedifference between syngas input to the anode and syngas output from theanode. Syngas may be used as an input, or fuel, for the anode, at leastin part. For example, a system may include an anode recycle loop thatreturns syngas from the anode exhaust to the anode inlet where it issupplemented with natural gas or other suitable fuel. Syngas producedLHV (sg net)=(LHV(sg out)−LHV(sg in)), where LHV(sg in) and LHV(sg out)refer to the LHV of the syngas in the anode inlet and syngas in theanode outlet streams or flows, respectively. It is noted that at least aportion of the syngas produced by the reforming reactions within ananode can typically be utilized in the anode to produce electricity. Thehydrogen utilized to produce electricity is not included in thedefinition of “syngas produced” because it does not exit the anode. Asused herein, the term “syngas ratio” is the LHV of the net syngasproduced divided by the LHV of the fuel input to the anode or LHV (sgnet)/LHV(anode in). Molar flow rates of syngas and fuel can be usedinstead of LHV to express a molar-based syngas ratio and a molar-basedsyngas produced.

Steam to carbon ratio (S/C): As used herein, the steam to carbon ratio(S/C) is the molar ratio of steam in a flow to reformable carbon in theflow. Carbon in the form of CO and CO₂ are not included as reformablecarbon in this definition. The steam to carbon ratio can be measuredand/or controlled at different points in the system. For example, thecomposition of an anode inlet stream can be manipulated to achieve a S/Cthat is suitable for reforming in the anode. The S/C can be given as themolar flow rate of H₂O divided by the product of the molar flow rate offuel multiplied by the number of carbon atoms in the fuel, e.g. one formethane. Thus, S/C=f_(H20)/(f_(CH4)×#C), where f_(H20) is the molar flowrate of water, where f_(CH4) is the molar flow rate of methane (or otherfuel) and #C is the number of carbons in the fuel.

EGR ratio: Aspects of the invention can use a turbine in partnershipwith a fuel cell. The combined fuel cell and turbine system may includeexhaust gas recycle (“EGR”). In an EGR system, at least a portion of theexhaust gas generated by the turbine can be sent to a heat recoverygenerator. Another portion of the exhaust gas can be sent to the fuelcell. The EGR ratio describes the amount of exhaust gas routed to thefuel cell versus the total exhaust gas routed to either the fuel cell orheat recovery generator. As used herein, the “EGR ratio” is the flowrate for the fuel cell bound portion of the exhaust gas divided by thecombined flow rate for the fuel cell bound portion and the recoverybound portion, which is sent to the heat recovery generator.

In various aspects of the invention, a molten carbonate fuel cell (MCFC)can be used to facilitate separation of CO₂ from a CO₂-containing streamwhile also generating additional electrical power. The CO₂ separationcan be further enhanced by taking advantage of synergies with thecombustion-based power generator that can provide at least a portion ofthe input feed to the cathode portion of the fuel cell.

Fuel Cell and Fuel Cell Components: In this discussion, a fuel cell cancorrespond to a single cell, with an anode and a cathode separated by anelectrolyte. The anode and cathode can receive input gas flows tofacilitate the respective anode and cathode reactions for transportingcharge across the electrolyte and generating electricity. A fuel cellstack can represent a plurality of cells in an integrated unit. Althougha fuel cell stack can include multiple fuel cells, the fuel cells cantypically be connected in parallel and can function (approximately) asif they collectively represented a single fuel cell of a larger size.When an input flow is delivered to the anode or cathode of a fuel cellstack, the fuel stack can include flow channels for dividing the inputflow between each of the cells in the stack and flow channels forcombining the output flows from the individual cells. In thisdiscussion, a fuel cell array can be used to refer to a plurality offuel cells (such as a plurality of fuel cell stacks) that are arrangedin series, in parallel, or in any other convenient manner (e.g., in acombination of series and parallel). A fuel cell array can include oneor more stages of fuel cells and/or fuel cell stacks, where theanode/cathode output from a first stage may serve as the anode/cathodeinput for a second stage. It is noted that the anodes in a fuel cellarray do not have to be connected in the same way as the cathodes in thearray. For convenience, the input to the first anode stage of a fuelcell array may be referred to as the anode input for the array, and theinput to the first cathode stage of the fuel cell array may be referredto as the cathode input to the array. Similarly, the output from thefinal anode/cathode stage may be referred to as the anode/cathode outputfrom the array.

It should be understood that reference to use of a fuel cell hereintypically denotes a “fuel cell stack” composed of individual fuel cells,and more generally refers to use of one or more fuel cell stacks influid communication. Individual fuel cell elements (plates) cantypically be “stacked” together in a rectangular array called a “fuelcell stack”. This fuel cell stack can typically take a feed stream anddistribute reactants among all of the individual fuel cell elements andcan then collect the products from each of these elements. When viewedas a unit, the fuel cell stack in operation can be taken as a whole eventhough composed of many (often tens or hundreds) of individual fuel cellelements. These individual fuel cell elements can typically have similarvoltages (as the reactant and product concentrations are similar), andthe total power output can result from the summation of all of theelectrical currents in all of the cell elements, when the elements areelectrically connected in series. Stacks can also be arranged in aseries arrangement to produce high voltages. A parallel arrangement canboost the current. If a sufficiently large volume fuel cell stack isavailable to process a given exhaust flow, the systems and methodsdescribed herein can be used with a single molten carbonate fuel cellstack. In other aspects of the invention, a plurality of fuel cellstacks may be desirable or needed for a variety of reasons.

For the purposes of this invention, unless otherwise specified, the term“fuel cell” should be understood to also refer to and/or is defined asincluding a reference to a fuel cell stack composed of set of one ormore individual fuel cell elements for which there is a single input andoutput, as that is the manner in which fuel cells are typically employedin practice. Similarly, the term fuel cells (plural), unless otherwisespecified, should be understood to also refer to and/or is defined asincluding a plurality of separate fuel cell stacks. In other words, allreferences within this document, unless specifically noted, can referinterchangeably to the operation of a fuel cell stack as a “fuel cell”.For example, the volume of exhaust generated by a commercial scale a)combustion generator may be too large for processing by a fuel cell(i.e., a single stack) of conventional size. In order to process thefull exhaust, a plurality of fuel cells (i.e., two or more separate fuelcells or fuel cell stacks) can be arranged in parallel, so that eachfuel cell can process (roughly) an equal portion of the combustionexhaust. Although multiple fuel cells can be used, each fuel cell cantypically be operated in a generally similar manner, given its (roughly)equal portion of the combustion exhaust.

“Internal reforming” and “external reforming”: A fuel cell or fuel cellstack may include one or more internal reforming sections. As usedherein, the term “internal reforming” refers to fuel reforming occurringwithin the body of a fuel cell, a fuel cell stack, or otherwise within afuel cell assembly. External reforming, which is often used inconjunction with a fuel cell, occurs in a separate piece of equipmentthat is located outside of the fuel cell stack. In other words, the bodyof the external reformer is not in direct physical contact with the bodyof a fuel cell or fuel cell stack. In a typical set up, the output fromthe external reformer can be fed to the anode inlet of a fuel cell.Unless otherwise noted specifically, the reforming described within thisapplication is internal reforming.

Internal reforming may occur within a fuel cell anode. Internalreforming can additionally or alternately occur within an internalreforming element integrated within a fuel cell assembly. The integratedreforming element may be located between fuel cell elements within afuel cell stack. In other words, one of the trays in the stack can be areforming section instead of a fuel cell element. In one aspect, theflow arrangement within a fuel cell stack directs fuel to the internalreforming elements and then into the anode portion of the fuel cells.Thus, from a flow perspective, the internal reforming elements and fuelcell elements can be arranged in series within the fuel cell stack. Asused herein, the term “anode reforming” is fuel reforming that occurswithin an anode. As used herein, the term “internal reforming” isreforming that occurs within an integrated reforming element and not inan anode section.

In some aspects, a reforming stage that is internal to a fuel cellassembly can be considered to be associated with the anode(s) in thefuel cell assembly. In some alternative aspects, for a reforming stagein a fuel cell stack that can be associated with an anode (such asassociated with multiple anodes), a flow path can be available so thatthe output flow from the reforming stage is passed into at least oneanode. This can correspond to having an initial section of a fuel cellplate not in contact with the electrolyte and instead can serve just asa reforming catalyst. Another option for an associated reforming stagecan be to have a separate integrated reforming stage as one of theelements in a fuel cell stack, where the output from the integratedreforming stage can be returned to the input side of one or more of thefuel cells in the fuel cell stack.

From a heat integration standpoint, a characteristic height in a fuelcell stack can be the height of an individual fuel cell stack element.It is noted that the separate reforming stage and/or a separateendothermic reaction stage could have a different height in the stackthan a fuel cell. In such a scenario, the height of a fuel cell elementcan be used as the characteristic height. In some aspects, an integratedendothermic reaction stage can be defined as a stage that is heatintegrated with one or more fuel cells, so that the integratedendothermic reaction stage can use the heat from the fuel cells as aheat source for the endothermic reaction. Such an integrated endothermicreaction stage can be defined as being positioned less than 5 times theheight of a stack element from any fuel cells providing heat to theintegrated stage. For example, an integrated endothermic reaction stage(such as a reforming stage) can be positioned less than 5 times theheight of a stack element from any fuel cells that are heat integrated,such as less than 3 times the height of a stack element. In thisdiscussion, an integrated reforming stage and/or integrated endothermicreaction stage that represent an adjacent stack element to a fuel cellelement can be defined as being about one stack element height or lessaway from the adjacent fuel cell element.

In some aspects, a separate reforming stage that is heat integrated witha fuel cell element can correspond to a reforming stage associated withthe fuel cell element. In such aspects, an integrated fuel cell elementcan provide at least a portion of the heat to the associated reformingstage, and the associated reforming stage can provide at least a portionof the reforming stage output to the integrated fuel cell as a fuelstream.

In other aspects, a separate reforming stage can be integrated with afuel cell for heat transfer without being associated with the fuel cell.In this type of situation, the separate reforming stage can receive heatfrom the fuel cell, but the decision can be made not to use the outputof the reforming stage as an input to the fuel cell. Instead, thedecision can be made to use the output of such a reforming stage foranother purpose, such as directly adding the output to the anode exhauststream, and/or for forming a separate output stream from the fuel cellassembly.

More generally, a separate stack element in a fuel cell stack can beused to perform any convenient type of endothermic reaction that cantake advantage of the waste heat provided by integrated fuel cell stackelements. Instead of plates suitable for performing a reforming reactionon a hydrocarbon fuel stream, a separate stack element can have platessuitable for catalyzing another type of endothermic reaction. A manifoldor other arrangement of inlet conduits in the fuel cell stack can beused to provide an appropriate input flow to each stack element. Asimilar manifold or other arrangement of outlet conduits canadditionally or alternately be used to withdraw the output flows fromeach stack element. Optionally, the output flows from a endothermicreaction stage in a stack can be withdrawn from the fuel cell stackwithout having the output flow pass through a fuel cell anode. In suchan optional aspect, the products of the exothermic reaction cantherefore exit from the fuel cell stack without passing through a fuelcell anode. Examples of other types of endothermic reactions that can beperformed in stack elements in a fuel cell stack can include, withoutlimitation, ethanol dehydration to form ethylene and ethane cracking.

Recycle: As defined herein, recycle of a portion of a fuel cell output(such as an anode exhaust or a stream separated or withdrawn from ananode exhaust) to a fuel cell inlet can correspond to a direct orindirect recycle stream. A direct recycle of a stream to a fuel cellinlet is defined as recycle of the stream without passing through anintermediate process, while an indirect recycle involves recycle afterpassing a stream through one or more intermediate processes. Forexample, if the anode exhaust is passed through a CO₂ separation stageprior to recycle, this is considered an indirect recycle of the anodeexhaust. If a portion of the anode exhaust, such as an H₂ streamwithdrawn from the anode exhaust, is passed into a gasifier forconverting coal into a fuel suitable for introduction into the fuelcell, then that is also considered an indirect recycle.

Anode Inputs and Outputs

In various aspects of the invention, the MCFC array can be fed by a fuelreceived at the anode inlet that comprises, for example, both hydrogenand a hydrocarbon such as methane (or alternatively a hydrocarbonaceousor hydrocarbon-like compound that may contain heteroatoms different fromC and H). Most of the methane (or other hydrocarbonaceous orhydrocarbon-like compound) fed to the anode can typically be freshmethane. In this description, a fresh fuel such as fresh methane refersto a fuel that is not recycled from another fuel cell process. Forexample, methane recycled from the anode outlet stream back to the anodeinlet may not be considered “fresh” methane, and can instead bedescribed as reclaimed methane. The fuel source used can be shared withother components, such as a turbine that uses a portion of the fuelsource to provide a CO₂-containing stream for the cathode input. Thefuel source input can include water in a proportion to the fuelappropriate for reforming the hydrocarbon (or hydrocarbon-like) compoundin the reforming section that generates hydrogen. For example, ifmethane is the fuel input for reforming to generate H₂, the molar ratioof water to fuel can be from about one to one to about ten to one, suchas at least about two to one. A ratio of four to one or greater istypical for external reforming, but lower values can be typical forinternal reforming. To the degree that H₂ is a portion of the fuelsource, in some optional aspects no additional water may be needed inthe fuel, as the oxidation of H₂ at the anode can tend to produce H₂Othat can be used for reforming the fuel. The fuel source can alsooptionally contain components incidental to the fuel source (e.g., anatural gas feed can contain some content of CO₂ as an additionalcomponent). For example, a natural gas feed can contain CO₂, N₂, and/orother inert (noble) gases as additional components. Optionally, in someaspects the fuel source may also contain CO, such as CO from a recycledportion of the anode exhaust. An additional or alternate potentialsource for CO in the fuel into a fuel cell assembly can be CO generatedby steam reforming of a hydrocarbon fuel performed on the fuel prior toentering the fuel cell assembly.

More generally, a variety of types of fuel streams may be suitable foruse as an input stream for the anode of a molten carbonate fuel cell.Some fuel streams can correspond to streams containing hydrocarbonsand/or hydrocarbon-like compounds that may also include heteroatomsdifferent from C and H. In this discussion, unless otherwise specified,a reference to a fuel stream containing hydrocarbons for an MCFC anodeis defined to include fuel streams containing such hydrocarbon-likecompounds. Examples of hydrocarbon (including hydrocarbon-like) fuelstreams include natural gas, streams containing C1-C4 carbon compounds(such as methane or ethane), and streams containing heavier C5+hydrocarbons (including hydrocarbon-like compounds), as well ascombinations thereof. Still other additional or alternate examples ofpotential fuel streams for use in an anode input can include biogas-typestreams, such as methane produced from natural (biological)decomposition of organic material.

In some aspects, a molten carbonate fuel cell can be used to process aninput fuel stream, such as a natural gas and/or hydrocarbon stream, witha low energy content due to the presence of diluent compounds. Forexample, some sources of methane and/or natural gas are sources that caninclude substantial amounts of either CO₂ or other inert molecules, suchas nitrogen, argon, or helium. Due to the presence of elevated amountsof CO₂ and/or inerts, the energy content of a fuel stream based on thesource can be reduced. Using a low energy content fuel for a combustionreaction (such as for powering a combustion-powered turbine) can posedifficulties. However, a molten carbonate fuel cell can generate powerbased on a low energy content fuel source with a reduced or minimalimpact on the efficiency of the fuel cell. The presence of additionalgas volume can require additional heat for raising the temperature ofthe fuel to the temperature for reforming and/or the anode reaction.Additionally, due to the equilibrium nature of the water gas shiftreaction within a fuel cell anode, the presence of additional CO₂ canhave an impact on the relative amounts of H₂ and CO present in the anodeoutput. However, the inert compounds otherwise can have only a minimaldirect impact on the reforming and anode reactions. The amount of CO₂and/or inert compounds in a fuel stream for a molten carbonate fuelcell, when present, can be at least about 1 vol %, such as at leastabout 2 vol %, or at least about 5 vol %, or at least about 10 vol %, orat least about 15 vol %, or at least about 20 vol %, or at least about25 vol %, or at least about 30 vol %, or at least about 35 vol %, or atleast about 40 vol %, or at least about 45 vol %, or at least about 50vol %, or at least about 75 vol %. Additionally or alternately, theamount of CO₂ and/or inert compounds in a fuel stream for a moltencarbonate fuel cell can be about 90 vol % or less, such as about 75 vol% or less, or about 60 vol % or less, or about 50 vol % or less, orabout 40 vol % or less, or about 35 vol % or less.

Yet other examples of potential sources for an anode input stream cancorrespond to refinery and/or other industrial process output streams.For example, coking is a common process in many refineries forconverting heavier compounds to lower boiling ranges. Coking typicallyproduces an off-gas containing a variety of compounds that are gases atroom temperature, including CO and various C1-C4 hydrocarbons. Thisoff-gas can be used as at least a portion of an anode input stream.Other refinery off-gas streams can additionally or alternately besuitable for inclusion in an anode input stream, such as light ends(C1-C4) generated during cracking or other refinery processes. Stillother suitable refinery streams can additionally or alternately includerefinery streams containing CO or CO₂ that also contain H₂ and/orreformable fuel compounds.

Still other potential sources for an anode input can additionally oralternately include streams with increased water content. For example,an ethanol output stream from an ethanol plant (or another type offermentation process) can include a substantial portion of H₂O prior tofinal distillation. Such H₂O can typically cause only minimal impact onthe operation of a fuel cell. Thus, a fermentation mixture of alcohol(or other fermentation product) and water can be used as at least aportion of an anode input stream.

Biogas, or digester gas, is another additional or alternate potentialsource for an anode input. Biogas may primarily comprise methane and CO₂and is typically produced by the breakdown or digestion of organicmatter. Anaerobic bacteria may be used to digest the organic matter andproduce the biogas. Impurities, such as sulfur-containing compounds, maybe removed from the biogas prior to use as an anode input.

The output stream from an MCFC anode can include H₂O, CO₂, CO, and H₂.Optionally, the anode output stream could also have unreacted fuel (suchas H₂ or CH₄) or inert compounds in the feed as additional outputcomponents. Instead of using this output stream as a fuel source toprovide heat for a reforming reaction or as a combustion fuel forheating the cell, one or more separations can be performed on the anodeoutput stream to separate the CO₂ from the components with potentialvalue as inputs to another process, such as H₂ or CO. The H₂ and/or COcan be used as a syngas for chemical synthesis, as a source of hydrogenfor chemical reaction, and/or as a fuel with reduced greenhouse gasemissions.

In various aspects, the composition of the output stream from the anodecan be impacted by several factors. Factors that can influence the anodeoutput composition can include the composition of the input stream tothe anode, the amount of current generated by the fuel cell, and/or thetemperature at the exit of the anode. The temperature of at the anodeexit can be relevant due to the equilibrium nature of the water gasshift reaction. In a typical anode, at least one of the plates formingthe wall of the anode can be suitable for catalyzing the water gas shiftreaction. As a result, if a) the composition of the anode input streamis known, b) the extent of reforming of reformable fuel in the anodeinput stream is known, and c) the amount of carbonate transported fromthe cathode to anode (corresponding to the amount of electrical currentgenerated) is known, the composition of the anode output can bedetermined based on the equilibrium constant for the water gas shiftreaction.K_(eq)=[CO₂][H₂]/[CO][H₂O]

In the above equation, K_(eq) is the equilibrium constant for thereaction at a given temperature and pressure, and [X] is the partialpressure of component X. Based on the water gas shift reaction, it canbe noted that an increased CO₂ concentration in the anode input can tendto result in additional CO formation (at the expense of H₂) while anincreased H₂O concentration can tend to result in additional H₂formation (at the expense of CO).

To determine the composition at the anode output, the composition of theanode input can be used as a starting point. This composition can thenbe modified to reflect the extent of reforming of any reformable fuelsthat can occur within the anode. Such reforming can reduce thehydrocarbon content of the anode input in exchange for increasedhydrogen and CO₂. Next, based on the amount of electrical currentgenerated, the amount of H₂ in the anode input can be reduced inexchange for additional H₂O and CO₂. This composition can then beadjusted based on the equilibrium constant for the water gas shiftreaction to determine the exit concentrations for H₂, CO, CO₂, and H₂O.

Table 1 shows the anode exhaust composition at different fuelutilizations for a typical type of fuel. The anode exhaust compositioncan reflect the combined result of the anode reforming reaction, watergas shift reaction, and the anode oxidation reaction. The outputcomposition values in Table 1 were calculated by assuming an anode inputcomposition with an about 2 to 1 ratio of steam (H₂O) to carbon(reformable fuel). The reformable fuel was assumed to be methane, whichwas assumed to be 100% reformed to hydrogen. The initial CO₂ and H₂concentrations in the anode input were assumed to be negligible, whilethe input N₂ concentration was about 0.5%. The fuel utilization U_(f)(as defined herein) was allowed to vary from about 35% to about 70% asshown in the table. The exit temperature for the fuel cell anode wasassumed to be about 650° C. for purposes of determining the correctvalue for the equilibrium constant.

TABLE 1 Anode Exhaust Composition Uf % 35% 40% 45% 50% 55% 60% 65% 70%Anode Exhaust Composition H₂O %, wet 32.5% 34.1% 35.5% 36.7% 37.8% 38.9%39.8% 40.5% CO₂ %, wet 26.7% 29.4% 32.0% 34.5% 36.9% 39.3% 41.5% 43.8%H₂ %, wet 29.4% 26.0% 22.9% 20.0% 17.3% 14.8% 12.5% 10.4% CO %, wet10.8% 10.0% 9.2% 8.4% 7.5% 6.7% 5.8% 4.9% N₂ %, wet 0.5% 0.5% 0.5% 0.4%0.4% 0.4% 0.4% 0.4% CO₂ %, dry 39.6% 44.6% 49.6% 54.5% 59.4% 64.2% 69.0%73.7% H₂ %, dry 43.6% 39.4% 35.4% 31.5% 27.8% 24.2% 20.7% 17.5% CO %,dry 16.1% 15.2% 14.3% 13.2% 12.1% 10.9% 9.7% 8.2% N₂ %, dry 0.7% 0.7%0.7% 0.7% 0.7% 0.7% 0.7% 0.7% H₂/CO 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.1 (H₂− CO₂)/ 0.07 −0.09 −0.22 −0.34 −0.44 −0.53 −0.61 −0.69 (CO + CO₂)

Table 1 shows anode output compositions for a particular set ofconditions and anode input composition. More generally, in variousaspects the anode output can include about 10 vol % to about 50 vol %H₂O. The amount of H₂O can vary greatly, as H₂O in the anode can beproduced by the anode oxidation reaction. If an excess of H₂O beyondwhat is needed for reforming is introduced into the anode, the excessH₂O can typically pass through largely unreacted, with the exception ofH₂O consumed (or generated) due to fuel reforming and the water gasshift reaction. The CO₂ concentration in the anode output can also varywidely, such as from about 20 vol % to about 50 vol % CO₂. The amount ofCO₂ can be influenced by both the amount of electrical current generatedas well as the amount of CO₂ in the anode input flow. The amount of H₂in the anode output can additionally or alternately be from about 10 vol% H₂ to about 50 vol % H₂, depending on the fuel utilization in theanode. At the anode output, the amount of CO can be from about 5 vol %to about 20 vol %. It is noted that the amount of CO relative to theamount of H₂ in the anode output for a given fuel cell can be determinedin part by the equilibrium constant for the water gas shift reaction atthe temperature and pressure present in the fuel cell. The anode outputcan further additionally or alternately include 5 vol % or less ofvarious other components, such as N₂, CH₄ (or other unreactedcarbon-containing fuels), and/or other components.

Optionally, one or more water gas shift reaction stages can be includedafter the anode output to convert CO and H₂O in the anode output intoCO₂ and H₂, if desired. The amount of H₂ present in the anode output canbe increased, for example, by using a water gas shift reactor at lowertemperature to convert H₂O and CO present in the anode output into H₂and CO₂. Alternatively, the temperature can be raised and the water-gasshift reaction can be reversed, producing more CO and H₂O from H₂ andCO₂. Water is an expected output of the reaction occurring at the anode,so the anode output can typically have an excess of H₂O relative to theamount of CO present in the anode output. Alternatively, H₂O can beadded to the stream after the anode exit but before the water gas shiftreaction. CO can be present in the anode output due to incomplete carbonconversion during reforming and/or due to the equilibrium balancingreactions between H₂O, CO, H₂, and CO₂ (i.e., the water-gas shiftequilibrium) under either reforming conditions or the conditions presentduring the anode reaction. A water gas shift reactor can be operatedunder conditions to drive the equilibrium further in the direction offorming CO₂ and H₂ at the expense of CO and H₂O. Higher temperatures cantend to favor the formation of CO and H₂O. Thus, one option foroperating the water gas shift reactor can be to expose the anode outputstream to a suitable catalyst, such as a catalyst including iron oxide,zinc oxide, copper on zinc oxide, or the like, at a suitabletemperature, e.g., between about 190° C. to about 210° C. Optionally,the water-gas shift reactor can include two stages for reducing the COconcentration in an anode output stream, with a first higher temperaturestage operated at a temperature from at least about 300° C. to about375° C. and a second lower temperature stage operated at a temperatureof about 225° C. or less, such as from about 180° C. to about 210° C. Inaddition to increasing the amount of H₂ present in the anode output, thewater-gas shift reaction can additionally or alternately increase theamount of CO₂ at the expense of CO. This can exchangedifficult-to-remove carbon monoxide (CO) for carbon dioxide, which canbe more readily removed by condensation (e.g., cryogenic removal),chemical reaction (such as amine removal), and/or other CO₂ removalmethods. Additionally or alternately, it may be desirable to increasethe CO content present in the anode exhaust in order to achieve adesired ratio of H₂ to CO.

After passing through the optional water gas shift reaction stage, theanode output can be passed through one or more separation stages forremoval of water and/or CO₂ from the anode output stream. For example,one or more CO₂ output streams can be formed by performing CO₂separation on the anode output using one or more methods individually orin combination. Such methods can be used to generate CO₂ outputstream(s) having a CO₂ content of 90 vol % or greater, such as at least95% vol % CO₂, or at least 98 vol % CO₂. Such methods can recover aboutat least about 70% of the CO₂ content of the anode output, such as atleast about 80% of the CO₂ content of the anode output, or at leastabout 90%. Alternatively, in some aspects it may be desirable to recoveronly a portion of the CO₂ within an anode output stream, with therecovered portion of CO₂ being about 33% to about 90% of the CO₂ in theanode output, such as at least about 40%, or at least about 50%. Forexample, it may be desirable to retain some CO₂ in the anode output flowso that a desired composition can be achieved in a subsequent water gasshift stage. Suitable separation methods may comprise use of a physicalsolvent (e.g., Selexol™ or Rectisol™); amines or other bases (e.g., MEAor MDEA); refrigeration (e.g., cryogenic separation); pressure swingadsorption; vacuum swing adsorption; and combinations thereof. Acryogenic CO₂ separator can be an example of a suitable separator. Asthe anode output is cooled, the majority of the water in the anodeoutput can be separated out as a condensed (liquid) phase. Furthercooling and/or pressurizing of the water-depleted anode output flow canthen separate high purity CO₂, as the other remaining components in theanode output flow (such as H₂, N₂, CH₄) do not tend to readily formcondensed phases. A cryogenic CO₂ separator can recover between about33% and about 90% of the CO₂ present in a flow, depending on theoperating conditions.

Removal of water from the anode exhaust to form one or more water outputstreams can also be beneficial, whether prior to, during, or afterperforming CO₂ separation. The amount of water in the anode output canvary depending on operating conditions selected. For example, thesteam-to-carbon ratio established at the anode inlet can affect thewater content in the anode exhaust, with high steam-to-carbon ratiostypically resulting in a large amount of water that can pass through theanode unreacted and/or reacted only due to the water gas shiftequilibrium in the anode. Depending on the aspect, the water content inthe anode exhaust can correspond to up to about 30% or more of thevolume in the anode exhaust. Additionally or alternately, the watercontent can be about 80% or less of the volume of the anode exhaust.While such water can be removed by compression and/or cooling withresulting condensation, the removal of this water can require extracompressor power and/or heat exchange surface area and excessive coolingwater. One beneficial way to remove a portion of this excess water canbe based on use of an adsorbent bed that can capture the humidity fromthe moist anode effluent and can then be ‘regenerated’ using dry anodefeed gas, in order to provide additional water for the anode feed.HVAC-style (heating, ventilation, and air conditioning) adsorptionwheels design can be applicable, because anode exhaust and inlet can besimilar in pressure, and minor leakage from one stream to the other canhave minimal impact on the overall process. In embodiments where CO₂removal is performed using a cryogenic process, removal of water priorto or during CO₂ removal may be desirable, including removal bytriethyleneglycol (TEG) system and/or desiccants. By contrast, if anamine wash is used for CO₂ removal, water can be removed from the anodeexhaust downstream from the CO₂ removal stage.

Alternately or in addition to a CO₂ output stream and/or a water outputstream, the anode output can be used to form one or more product streamscontaining a desired chemical or fuel product. Such a product stream orstreams can correspond to a syngas stream, a hydrogen stream, or bothsyngas product and hydrogen product streams. For example, a hydrogenproduct stream containing at least about 70 vol % H₂, such as at leastabout 90 vol % H₂ or at least about 95 vol % H₂, can be formed.Additionally or alternately, a syngas stream containing at least about70 vol % of H₂ and CO combined, such as at least about 90 vol % of H₂and CO can be formed. The one or more product streams can have a gasvolume corresponding to at least about 75% of the combined H₂ and CO gasvolumes in the anode output, such as at least about 85% or at leastabout 90% of the combined H₂ and CO gas volumes. It is noted that therelative amounts of H₂ and CO in the products streams may differ fromthe H₂ to CO ratio in the anode output based on use of water gas shiftreaction stages to convert between the products.

In some aspects, it can be desirable to remove or separate a portion ofthe H₂ present in the anode output. For example, in some aspects the H₂to CO ratio in the anode exhaust can be at least about 3.0:1. Bycontrast, processes that make use of syngas, such as Fischer-Tropschsynthesis, may consume H₂ and CO in a different ratio, such as a ratiothat is closer to 2:1. One alternative can be to use a water gas shiftreaction to modify the content of the anode output to have an H₂ to COratio closer to a desired syngas composition. Another alternative can beto use a membrane separation to remove a portion of the H₂ present inthe anode output to achieve a desired ratio of H₂ and CO, or stillalternately to use a combination of membrane separation and water gasshift reactions. One advantage of using a membrane separation to removeonly a portion of the H₂ in the anode output can be that the desiredseparation can be performed under relatively mild conditions. Since onegoal can be to produce a retentate that still has a substantial H₂content, a permeate of high purity hydrogen can be generated by membraneseparation without requiring severe conditions. For example, rather thanhaving a pressure on the permeate side of the membrane of about 100 kPaaor less (such as ambient pressure), the permeate side can be at anelevated pressure relative to ambient while still having sufficientdriving force to perform the membrane separation. Additionally oralternately, a sweep gas such as methane can be used to provide adriving force for the membrane separation. This can reduce the purity ofthe H₂ permeate stream, but may be advantageous, depending on thedesired use for the permeate stream.

In various aspects of the invention, at least a portion of the anodeexhaust stream (preferably after separation of CO₂ and/or H₂O) can beused as a feed for a process external to the fuel cell and associatedreforming stages. In various aspects, the anode exhaust can have a ratioof H₂ to CO of about 1.5:1 to about 10:1, such as at least about 3.0:1,or at least about 4.0:1, or at least about 5.0:1. A syngas stream can begenerated or withdrawn from the anode exhaust. The anode exhaust gas,optionally after separation of CO₂ and/or H₂O, and optionally afterperforming a water gas shift reaction and/or a membrane separation toremove excess hydrogen, can correspond to a stream containingsubstantial portions of H₂ and/or CO. For a stream with a relatively lowcontent of CO, such as a stream where the ratio of H₂ to CO is at leastabout 3:1, the anode exhaust can be suitable for use as an H₂ feed.Examples of processes that could benefit from an H₂ feed can include,but are not limited to, refinery processes, an ammonia synthesis plant,or a turbine in a (different) power generation system, or combinationsthereof. Depending on the application, still lower CO₂ contents can bedesirable. For a stream with an H₂-to-CO ratio of less than about 2.2 to1 and greater than about 1.9 to 1, the stream can be suitable for use asa syngas feed. Examples of processes that could benefit from a syngasfeed can include, but are not limited to, a gas-to-liquids plant (suchas a plant using a Fischer-Tropsch process with a non-shifting catalyst)and/or a methanol synthesis plant. The amount of the anode exhaust usedas a feed for an external process can be any convenient amount.Optionally, when a portion of the anode exhaust is used as a feed for anexternal process, a second portion of the anode exhaust can be recycledto the anode input and/or recycled to the combustion zone for acombustion-powered generator.

The input streams useful for different types of Fischer-Tropschsynthesis processes can provide an example of the different types ofproduct streams that may be desirable to generate from the anode output.For a Fischer-Tropsch synthesis reaction system that uses a shiftingcatalyst, such as an iron-based catalyst, the desired input stream tothe reaction system can include CO₂ in addition to H₂ and CO. If asufficient amount of CO₂ is not present in the input stream, aFischer-Tropsch catalyst with water gas shift activity can consume CO inorder to generate additional CO₂, resulting in a syngas that can bedeficient in CO. For integration of such a Fischer-Tropsch process withan MCFC fuel cell, the separation stages for the anode output can beoperated to retain a desired amount of CO₂ (and optionally H₂O) in thesyngas product. By contrast, for a Fischer-Tropsch catalyst based on anon-shifting catalyst, any CO₂ present in a product stream could serveas an inert component in the Fischer-Tropsch reaction system.

In an aspect where the membrane is swept with a sweep gas such as amethane sweep gas, the methane sweep gas can correspond to a methanestream used as the anode fuel or in a different low pressure process,such as a boiler, furnace, gas turbine, or other fuel-consuming device.In such an aspect, low levels of CO₂ permeation across the membrane canhave minimal consequence. Such CO₂ that may permeate across the membranecan have a minimal impact on the reactions within the anode, and suchCO₂ can remain contained in the anode product. Therefore, the CO₂ (ifany) lost across the membrane due to permeation does not need to betransferred again across the MCFC electrolyte. This can significantlyreduce the separation selectivity requirement for the hydrogenpermeation membrane. This can allow, for example, use of ahigher-permeability membrane having a lower selectivity, which canenable use of a lower pressure and/or reduced membrane surface area. Insuch an aspect of the invention, the volume of the sweep gas can be alarge multiple of the volume of hydrogen in the anode exhaust, which canallow the effective hydrogen concentration on the permeate side to bemaintained close to zero. The hydrogen thus separated can beincorporated into the turbine-fed methane where it can enhance theturbine combustion characteristics, as described above.

It is noted that excess H₂ produced in the anode can represent a fuelwhere the greenhouse gases have already been separated. Any CO₂ in theanode output can be readily separated from the anode output, such as byusing an amine wash, a cryogenic CO₂ separator, and/or a pressure orvacuum swing absorption process. Several of the components of the anodeoutput (H₂, CO, CH₄) are not easily removed, while CO₂ and H₂O canusually be readily removed. Depending on the embodiment, at least about90 vol % of the CO₂ in the anode output can be separated out to form arelatively high purity CO₂ output stream. Thus, any CO₂ generated in theanode can be efficiently separated out to form a high purity CO₂ outputstream. After separation, the remaining portion of the anode output cancorrespond primarily to components with chemical and/or fuel value, aswell as reduced amounts of CO₂ and/or H₂O, Since a substantial portionof the CO₂ generated by the original fuel (prior to reforming) can havebeen separated out, the amount of CO₂ generated by subsequent burning ofthe remaining portion of the anode output can be reduced. In particular,to the degree that the fuel in the remaining portion of the anode outputis H₂, no additional greenhouse gases can typically be formed by burningof this fuel.

The anode exhaust can be subjected to a variety of gas processingoptions, including water-gas shift and separation of the components fromeach other. Two general anode processing schemes are shown in FIGS. 1and 2.

FIG. 1 schematically shows an example of a reaction system for operatinga fuel cell array of molten carbonate fuel cells in conjunction with achemical synthesis process. In FIG. 1, a fuel stream 105 is provided toa reforming stage (or stages) 110 associated with the anode 127 of afuel cell 120, such as a fuel cell that is part of a fuel cell stack ina fuel cell array. The reforming stage 110 associated with fuel cell 120can be internal to a fuel cell assembly. In some optional aspects, anexternal reforming stage (not shown) can also be used to reform aportion of the reformable fuel in an input stream prior to passing theinput stream into a fuel cell assembly. Fuel stream 105 can preferablyinclude a reformable fuel, such as methane, other hydrocarbons, and/orother hydrocarbon-like compounds such as organic compounds containingcarbon-hydrogen bonds. Fuel stream 105 can also optionally contain H₂and/or CO, such as H₂ and/or CO provided by optional anode recyclestream 185. It is noted that anode recycle stream 185 is optional, andthat in many aspects no recycle stream is provided from the anodeexhaust 125 back to anode 127, either directly or indirectly viacombination with fuel stream 105 or reformed fuel stream 115. Afterreforming, the reformed fuel stream 115 can be passed into anode 127 offuel cell 120. A CO₂ and O₂-containing stream 119 can also be passedinto cathode 129. A flow of carbonate ions 122, CO₃ ²⁻, from the cathodeportion 129 of the fuel cell can provide the remaining reactant neededfor the anode fuel cell reactions. Based on the reactions in the anode127, the resulting anode exhaust 125 can include H₂O, CO₂, one or morecomponents corresponding to incompletely reacted fuel (H₂, CO, CH₄, orother components corresponding to a reformable fuel), and optionally oneor more additional nonreactive components, such as N₂ and/or othercontaminants that are part of fuel stream 105. The anode exhaust 125 canthen be passed into one or more separation stages. For example, a CO₂removal stage 140 can correspond to a cryogenic CO₂ removal system, anamine wash stage for removal of acid gases such as CO₂, or anothersuitable type of CO₂ separation stage for separating a CO₂ output stream143 from the anode exhaust. Optionally, the anode exhaust can first bepassed through a water gas shift reactor 130 to convert any CO presentin the anode exhaust (along with some H₂O) into CO₂ and H₂ in anoptionally water gas shifted anode exhaust 135. Depending on the natureof the CO₂ removal stage, a water condensation or removal stage 150 maybe desirable to remove a water output stream 153 from the anode exhaust.Though shown in FIG. 1 after the CO₂ separation stage 140, it mayoptionally be located before the CO₂ separation stage 140 instead.Additionally, an optional membrane separation stage 160 for separationof H₂ can be used to generate a high purity permeate stream 163 of H₂.The resulting retentate stream 166 can then be used as an input to achemical synthesis process. Stream 166 could additionally or alternatelybe shifted in a second water-gas shift reactor 131 to adjust the H₂, CO,and CO₂ content to a different ratio, producing an output stream 168 forfurther use in a chemical synthesis process. In FIG. 1, anode recyclestream 185 is shown as being withdrawn from the retentate stream 166,but the anode recycle stream 185 could additionally or alternately bewithdrawn from other convenient locations in or between the variousseparation stages. The separation stages and shift reactor(s) couldadditionally or alternately be configured in different orders, and/or ina parallel configuration. Finally, a stream with a reduced content ofCO₂ 139 can be generated as an output from cathode 129. For the sake ofsimplicity, various stages of compression and heat addition/removal thatmight be useful in the process, as well as steam addition or removal,are not shown.

As noted above, the various types of separations performed on the anodeexhaust can be performed in any convenient order. FIG. 2 shows anexample of an alternative order for performing separations on an anodeexhaust. In FIG. 2, anode exhaust 125 can be initially passed intoseparation stage 260 for removing a portion 263 of the hydrogen contentfrom the anode exhaust 125. This can allow, for example, reduction ofthe H₂ content of the anode exhaust to provide a retentate 266 with aratio of H₂ to CO closer to 2:1. The ratio of H₂ to CO can then befurther adjusted to achieve a desired value in a water gas shift stage230. The water gas shifted output 235 can then pass through CO₂separation stage 240 and water removal stage 250 to produce an outputstream 275 suitable for use as an input to a desired chemical synthesisprocess. Optionally, output stream 275 could be exposed to an additionalwater gas shift stage (not shown). A portion of output stream 275 canoptionally be recycled (not shown) to the anode input. Of course, stillother combinations and sequencing of separation stages can be used togenerate a stream based on the anode output that has a desiredcomposition. For the sake of simplicity, various stages of compressionand heat addition/removal that might be useful in the process, as wellas steam addition or removal, are not shown.

Cathode Inputs and Outputs

Conventionally, a molten carbonate fuel cell can be operated based ondrawing a desired load while consuming some portion of the fuel in thefuel stream delivered to the anode. The voltage of the fuel cell canthen be determined by the load, fuel input to the anode, air and CO₂provided to the cathode, and the internal resistances of the fuel cell.The CO₂ to the cathode can be conventionally provided in part by usingthe anode exhaust as at least a part of the cathode input stream. Bycontrast, the present invention can use separate/different sources forthe anode input and cathode input. By removing any direct link betweenthe composition of the anode input flow and the cathode input flow,additional options become available for operating the fuel cell, such asto generate excess synthesis gas, to improve capture of carbon dioxide,and/or to improve the total efficiency (electrical plus chemical power)of the fuel cell, among others.

In a molten carbonate fuel cell, the transport of carbonate ions acrossthe electrolyte in the fuel cell can provide a method for transportingCO₂ from a first flow path to a second flow path, where the transportmethod can allow transport from a lower concentration (the cathode) to ahigher concentration (the anode), which can thus facilitate capture ofCO₂. Part of the selectivity of the fuel cell for CO₂ separation can bebased on the electrochemical reactions allowing the cell to generateelectrical power. For nonreactive species (such as N₂) that effectivelydo not participate in the electrochemical reactions within the fuelcell, there can be an insignificant amount of reaction and transportfrom cathode to anode. By contrast, the potential (voltage) differencebetween the cathode and anode can provide a strong driving force fortransport of carbonate ions across the fuel cell. As a result, thetransport of carbonate ions in the molten carbonate fuel cell can allowCO₂ to be transported from the cathode (lower CO₂ concentration) to theanode (higher CO₂ concentration) with relatively high selectivity.However, a challenge in using molten carbonate fuel cells for carbondioxide removal can be that the fuel cells have limited ability toremove carbon dioxide from relatively dilute cathode feeds. The voltageand/or power generated by a carbonate fuel cell can start to droprapidly as the CO₂ concentration falls below about 2.0 vol %. As the CO₂concentration drops further, e.g., to below about 1.0 vol %, at somepoint the voltage across the fuel cell can become low enough that littleor no further transport of carbonate may occur and the fuel cell ceasesto function. Thus, at least some CO₂ is likely to be present in theexhaust gas from the cathode stage of a fuel cell under commerciallyviable operating conditions.

The amount of carbon dioxide delivered to the fuel cell cathode(s) canbe determined based on the CO₂ content of a source for the cathodeinlet. One example of a suitable CO₂-containing stream for use as acathode input flow can be an output or exhaust flow from a combustionsource. Examples of combustion sources include, but are not limited to,sources based on combustion of natural gas, combustion of coal, and/orcombustion of other hydrocarbon-type fuels (including biologicallyderived fuels). Additional or alternate sources can include other typesof boilers, fired heaters, furnaces, and/or other types of devices thatburn carbon-containing fuels in order to heat another substance (such aswater or air). To a first approximation, the CO₂ content of the outputflow from a combustion source can be a minor portion of the flow. Evenfor a higher CO₂ content exhaust flow, such as the output from acoal-fired combustion source, the CO₂ content from most commercialcoal-fired power plants can be about 15 vol % or less. More generally,the CO₂ content of an output or exhaust flow from a combustion sourcecan be at least about 1.5 vol %, or at least about 1.6 vol %, or atleast about 1.7 vol %, or at least about 1.8 vol %, or at least about1.9 vol %, or at least greater 2 vol %, or at least about 4 vol %, or atleast about 5 vol %, or at least about 6 vol %, or at least about 8 vol%. Additionally or alternately, the CO₂ content of an output or exhaustflow from a combustion source can be about 20 vol % or less, such asabout 15 vol % or less, or about 12 vol % or less, or about 10 vol % orless, or about 9 vol % or less, or about 8 vol % or less, or about 7 vol% or less, or about 6.5 vol % or less, or about 6 vol % or less, orabout 5.5 vol % or less, or about 5 vol % or less, or about 4.5 vol % orless. The concentrations given above are on a dry basis. It is notedthat the lower CO₂ content values can be present in the exhaust fromsome natural gas or methane combustion sources, such as generators thatare part of a power generation system that may or may not include anexhaust gas recycle loop.

Other potential sources for a cathode input stream can additionally oralternately include sources of bio-produced CO₂. This can include, forexample, CO₂ generated during processing of bio-derived compounds, suchas CO₂ generated during ethanol production. An additional or alternateexample can include CO₂ generated by combustion of a bio-produced fuel,such as combustion of lignocellulose. Still other additional oralternate potential CO₂ sources can correspond to output or exhauststreams from various industrial processes, such as CO₂-containingstreams generated by plants for manufacture of steel, cement, and/orpaper.

Yet another additional or alternate potential source of CO₂ can beCO₂-containing streams from a fuel cell. The CO₂-containing stream froma fuel cell can correspond to a cathode output stream from a differentfuel cell, an anode output stream from a different fuel cell, a recyclestream from the cathode output to the cathode input of a fuel cell,and/or a recycle stream from an anode output to a cathode input of afuel cell. For example, an MCFC operated in standalone mode underconventional conditions can generate a cathode exhaust with a CO₂concentration of at least about 5 vol %. Such a CO₂-containing cathodeexhaust could be used as a cathode input for an MCFC operated accordingto an aspect of the invention. More generally, other types of fuel cellsthat generate a CO₂ output from the cathode exhaust can additionally oralternately be used, as well as other types of CO₂-containing streamsnot generated by a “combustion” reaction and/or by a combustion-poweredgenerator. Optionally but preferably, a CO₂-containing stream fromanother fuel cell can be from another molten carbonate fuel cell. Forexample, for molten carbonate fuel cells connected in series withrespect to the cathodes, the output from the cathode for a first moltencarbonate fuel cell can be used as the input to the cathode for a secondmolten carbonate fuel cell.

For various types of CO₂-containing streams from sources other thancombustion sources, the CO₂ content of the stream can vary widely. TheCO₂ content of an input stream to a cathode can contain at least about 2vol % of CO₂, such as at least about 4 vol %, or at least about 5 vol %,or at least about 6 vol %, or at least about 8 vol %. Additionally oralternately, the CO₂ content of an input stream to a cathode can beabout 30 vol % or less, such as about 25 vol % or less, or about 20 vol% or less, or about 15 vol % or less, or about 10 vol % or less, orabout 8 vol % or less, or about 6 vol % or less, or about 4 vol % orless. For some still higher CO₂ content streams, the CO₂ content can begreater than about 30 vol %, such as a stream substantially composed ofCO₂ with only incidental amounts of other compounds. As an example, agas-fired turbine without exhaust gas recycle can produce an exhauststream with a CO₂ content of approximately 4.2 vol %. With EGR, agas-fired turbine can produce an exhaust stream with a CO₂ content ofabout 6-8 vol %. Stoichiometric combustion of methane can produce anexhaust stream with a CO₂ content of about 11 vol %. Combustion of coalcan produce an exhaust stream with a CO₂ content of about 15-20 vol %.Fired heaters using refinery off-gas can produce an exhaust stream witha CO₂ content of about 12-15 vol %. A gas turbine operated on a low BTUgas without any EGR can produce an exhaust stream with a CO₂ content of˜12 vol %.

In addition to CO₂, a cathode input stream must include O₂ to providethe components necessary for the cathode reaction. Some cathode inputstreams can be based on having air as a component. For example, acombustion exhaust stream can be formed by combusting a hydrocarbon fuelin the presence of air. Such a combustion exhaust stream, or anothertype of cathode input stream having an oxygen content based on inclusionof air, can have an oxygen content of about 20 vol % or less, such asabout 15 vol % or less, or about 10 vol % or less. Additionally oralternately, the oxygen content of the cathode input stream can be atleast about 4 vol %, such as at least about 6 vol %, or at least about 8vol %. More generally, a cathode input stream can have a suitablecontent of oxygen for performing the cathode reaction. In some aspects,this can correspond to an oxygen content of about 5 vol % to about 15vol %, such as from about 7 vol % to about 9 vol %. For many types ofcathode input streams, the combined amount of CO₂ and O₂ can correspondto less than about 21 vol % of the input stream, such as less than about15 vol % of the stream or less than about 10 vol % of the stream. An airstream containing oxygen can be combined with a CO₂ source that has lowoxygen content. For example, the exhaust stream generated by burningcoal may include a low oxygen content that can be mixed with air to forma cathode inlet stream.

In addition to CO₂ and O₂, a cathode input stream can also be composedof inert/non-reactive species such as N₂, H₂O, and other typical oxidant(air) components. For example, for a cathode input derived from anexhaust from a combustion reaction, if air is used as part of theoxidant source for the combustion reaction, the exhaust gas can includetypical components of air such as N₂, H₂O, and other compounds in minoramounts that are present in air. Depending on the nature of the fuelsource for the combustion reaction, additional species present aftercombustion based on the fuel source may include one or more of H₂O,oxides of nitrogen (NOx) and/or sulfur (SOx), and other compounds eitherpresent in the fuel and/or that are partial or complete combustionproducts of compounds present in the fuel, such as CO. These species maybe present in amounts that do not poison the cathode catalyst surfacesthough they may reduce the overall cathode activity. Such reductions inperformance may be acceptable, or species that interact with the cathodecatalyst may be reduced to acceptable levels by known pollutant removaltechnologies.

The amount of O₂ present in a cathode input stream (such as an inputcathode stream based on a combustion exhaust) can advantageously besufficient to provide the oxygen needed for the cathode reaction in thefuel cell. Thus, the volume percentage of O₂ can advantageously be atleast 0.5 times the amount of CO₂ in the exhaust. Optionally, asnecessary, additional air can be added to the cathode input to providesufficient oxidant for the cathode reaction. When some form of air isused as the oxidant, the amount of N₂ in the cathode exhaust can be atleast about 78 vol %, e.g., at least about 88 vol %, and/or about 95 vol% or less. In some aspects, the cathode input stream can additionally oralternately contain compounds that are generally viewed as contaminants,such as H₂S or NH₃. In other aspects, the cathode input stream can becleaned to reduce or minimize the content of such contaminants.

In addition to the reaction to form carbonate ions for transport acrossthe electrolyte, the conditions in the cathode can also be suitable forconversion of nitrogen oxides into nitrate and/or nitrate ions.Hereinafter, only nitrate ions will be referred to for convenience. Theresulting nitrate ions can also be transported across the electrolytefor reaction in the anode. NOx concentrations in a cathode input streamcan typically be on the order of ppm, so this nitrate transport reactioncan have a minimal impact on the amount of carbonate transported acrossthe electrolyte. However, this method of NOx removal can be beneficialfor cathode input streams based on combustion exhausts from gasturbines, as this can provide a mechanism for reducing NOx emissions.The conditions in the cathode can additionally or alternately besuitable for conversion of unburned hydrocarbons (in combination with O₂in the cathode input stream) to typical combustion products, such as CO₂and H₂O.

A suitable temperature for operation of an MCFC can be between about450° C. and about 750° C., such as at least about 500° C., e.g., with aninlet temperature of about 550° C. and an outlet temperature of about625° C. Prior to entering the cathode, heat can be added to or removedfrom the combustion exhaust, if desired, e.g., to provide heat for otherprocesses, such as reforming the fuel input for the anode. For example,if the source for the cathode input stream is a combustion exhauststream, the combustion exhaust stream may have a temperature greaterthan a desired temperature for the cathode inlet. In such an aspect,heat can be removed from the combustion exhaust prior to use as thecathode input stream. Alternatively, the combustion exhaust could be atvery low temperature, for example after a wet gas scrubber on acoal-fired boiler, in which case the combustion exhaust can be belowabout 100° C. Alternatively, the combustion exhaust could be from theexhaust of a gas turbine operated in combined cycle mode, in which thegas can be cooled by raising steam to run a steam turbine for additionalpower generation. In this case, the gas can be below about 50° C. Heatcan be added to a combustion exhaust that is cooler than desired.

Fuel Cell Arrangement

In various aspects, a configuration option for a fuel cell (such as afuel cell array containing multiple fuel cell stacks) can be to dividethe CO₂-containing stream between a plurality of fuel cells. Some typesof sources for CO₂-containing streams can generate large volumetric flowrates relative to the capacity of an individual fuel cell. For example,the CO₂-containing output stream from an industrial combustion sourcecan typically correspond to a large flow volume relative to desirableoperating conditions for a single MCFC of reasonable size. Instead ofprocessing the entire flow in a single MCFC, the flow can be dividedamongst a plurality of MCFC units, usually at least some of which can bein parallel, so that the flow rate in each unit can be within a desiredflow range.

A second configuration option can be to utilize fuel cells in series tosuccessively remove CO₂ from a flow stream. Regardless of the number ofinitial fuel cells to which a CO₂-containing stream can be distributedto in parallel, each initial fuel cell can be followed by one or moreadditional cells in series to further remove additional CO₂. If thedesired amount of CO₂ in the cathode output is sufficiently low,attempting to remove CO₂ from a cathode input stream down to the desiredlevel in a single fuel cell or fuel cell stage could lead to a lowand/or unpredictable voltage output for the fuel cell. Rather thanattempting to remove CO₂ to the desired level in a single fuel cell orfuel cell stage, CO₂ can be removed in successive cells until a desiredlevel can be achieved. For example, each cell in a series of fuel cellscan be used to remove some percentage (e.g., about 50%) of the CO₂present in a fuel stream. In such an example, if three fuel cells areused in series, the CO₂ concentration can be reduced (e.g., to about 15%or less of the original amount present, which can correspond to reducingthe CO₂ concentration from about 6% to about 1% or less over the courseof three fuel cells in series).

In another configuration, the operating conditions can be selected inearly fuel stages in series to provide a desired output voltage whilethe array of stages can be selected to achieve a desired level of carbonseparation. As an example, an array of fuel cells can be used with threefuel cells in series. The first two fuel cells in series can be used toremove CO₂ while maintaining a desired output voltage. The final fuelcell can then be operated to remove CO₂ to a desired concentration butat a lower voltage.

In still another configuration, there can be separate connectivity forthe anodes and cathodes in a fuel cell array. For example, if the fuelcell array includes fuel cathodes connected in series, the correspondinganodes can be connected in any convenient manner, not necessarilymatching up with the same arrangement as their corresponding cathodes,for example. This can include, for instance, connecting the anodes inparallel, so that each anode receives the same type of fuel feed, and/orconnecting the anodes in a reverse series, so that the highest fuelconcentration in the anodes can correspond to those cathodes having thelowest CO₂ concentration.

In yet another configuration, the amount of fuel delivered to one ormore anode stages and/or the amount of CO₂ delivered to one or morecathode stages can be controlled in order to improve the performance ofthe fuel cell array. For example, a fuel cell array can have a pluralityof cathode stages connected in series. In an array that includes threecathode stages in series, this can mean that the output from a firstcathode stage can correspond to the input for a second cathode stage,and the output from the second cathode stage can correspond to the inputfor a third cathode stage. In this type of configuration, the CO₂concentration can decrease with each successive cathode stage. Tocompensate for this reduced CO₂ concentration, additional hydrogenand/or methane can be delivered to the anode stages corresponding to thelater cathode stages. The additional hydrogen and/or methane in theanodes corresponding to the later cathode stages can at least partiallyoffset the loss of voltage and/or current caused by the reduced CO₂concentration, which can increase the voltage and thus net powerproduced by the fuel cell. In another example, the cathodes in a fuelcell array can be connected partially in series and partially inparallel. In this type of example, instead of passing the entirecombustion output into the cathodes in the first cathode stage, at leasta portion of the combustion exhaust can be passed into a later cathodestage. This can provide an increased CO₂ content in a later cathodestage. Still other options for using variable feeds to either anodestages or cathode stages can be used if desired.

The cathode of a fuel cell can correspond to a plurality of cathodesfrom an array of fuel cells, as previously described. In some aspects, afuel cell array can be operated to improve or maximize the amount ofcarbon transferred from the cathode to the anode. In such aspects, forthe cathode output from the final cathode(s) in an array sequence(typically at least including a series arrangement, or else the finalcathode(s) and the initial cathode(s) would be the same), the outputcomposition can include about 2.0 vol % or less of CO₂ (e.g., about 1.5vol % or less or about 1.2 vol % or less) and/or at least about 0.5 vol% of CO₂, or at least about 1.0 vol %, or at least about 1.2 vol % or atleast about 1.5 vol %. Due to this limitation, the net efficiency of CO₂removal when using molten carbonate fuel cells can be dependent on theamount of CO₂ in the cathode input. For cathode input streams with CO₂contents of greater than about 6 vol %, such as at least about 8%, thelimitation on the amount of CO₂ that can be removed is not severe.However, for a combustion reaction using natural gas as a fuel and withexcess air, as is typically found in a gas turbine, the amount of CO₂ inthe combustion exhaust may only correspond to a CO₂ concentration at thecathode input of less than about 5 vol %. Use of exhaust gas recycle canallow the amount of CO₂ at the cathode input to be increased to at leastabout 5 vol %, e.g., at least about 6 vol %. If EGR is increased whenusing natural gas as a fuel to produce a CO₂ concentration beyond about6 vol %, then the flammability in the combustor can be decreased and thegas turbine may become unstable. However, when H₂ is added to the fuel,the flammability window can be significantly increased, allowing theamount of exhaust gas recycle to be increased further, so thatconcentrations of CO₂ at the cathode input of at least about 7.5 vol %or at least about 8 vol % can be achieved. As an example, based on aremoval limit of about 1.5 vol % at the cathode exhaust, increasing theCO₂ content at the cathode input from about 5.5 vol % to about 7.5 vol %can correspond to a ˜10% increase in the amount of CO₂ that can becaptured using a fuel cell and transported to the anode loop foreventual CO₂ separation. The amount of O₂ in the cathode output canadditionally or alternately be reduced, typically in an amountproportional to the amount of CO₂ removed, which can result in smallcorresponding increases in the amount(s) of the other(non-cathode-reactive) species at the cathode exit.

In other aspects, a fuel cell array can be operated to improve ormaximize the energy output of the fuel cell, such as the total energyoutput, the electric energy output, the syngas chemical energy output,or a combination thereof. For example, molten carbonate fuel cells canbe operated with an excess of reformable fuel in a variety ofsituations, such as for generation of a syngas stream for use inchemical synthesis plant and/or for generation of a high purity hydrogenstream. The syngas stream and/or hydrogen stream can be used as a syngassource, a hydrogen source, as a clean fuel source, and/or for any otherconvenient application. In such aspects, the amount of CO₂ in thecathode exhaust can be related to the amount of CO₂ in the cathode inputstream and the CO₂ utilization at the desired operating conditions forimproving or maximizing the fuel cell energy output.

Additionally or alternately, depending on the operating conditions, anMCFC can lower the CO₂ content of a cathode exhaust stream to about 5.0vol % or less, e.g., about 4.0 vol % or less, or about 2.0 vol % orless, or about 1.5 vol % or less, or about 1.2 vol % or less.Additionally or alternately, the CO₂ content of the cathode exhauststream can be at least about 0.9 vol %, such as at least about 1.0 vol%, or at least about 1.2 vol %, or at least about 1.5 vol %.

Molten Carbonate Fuel Cell Operation

In some aspects, a fuel cell may be operated in a single pass oronce-through mode. In single pass mode, reformed products in the anodeexhaust are not returned to the anode inlet. Thus, recycling syngas,hydrogen, or some other product from the anode output directly to theanode inlet is not done in single pass operation. More generally, insingle pass operation, reformed products in the anode exhaust are alsonot returned indirectly to the anode inlet, such as by using reformedproducts to process a fuel stream subsequently introduced into the anodeinlet. Optionally, CO₂ from the anode outlet can be recycled to thecathode inlet during operation of an MCFC in single pass mode. Moregenerally, in some alternative aspects, recycling from the anode outletto the cathode inlet may occur for an MCFC operating in single passmode. Heat from the anode exhaust or output may additionally oralternately be recycled in a single pass mode. For example, the anodeoutput flow may pass through a heat exchanger that cools the anodeoutput and warms another stream, such as an input stream for the anodeand/or the cathode. Recycling heat from anode to the fuel cell isconsistent with use in single pass or once-through operation. Optionallybut not preferably, constituents of the anode output may be burned toprovide heat to the fuel cell during single pass mode.

FIG. 3 shows a schematic example of the operation of an MCFC forgeneration of electrical power. In FIG. 3, the anode portion of the fuelcell can receive fuel and steam (H₂O) as inputs, with outputs of water,CO₂, and optionally excess H₂, CH₄ (or other hydrocarbons), and/or CO.The cathode portion of the fuel cell can receive CO₂ and some oxidant(e.g., air/O₂) as inputs, with an output corresponding to a reducedamount of CO₂ in O₂-depleted oxidant (air). Within the fuel cell, CO₃ ²⁻ions formed in the cathode side can be transported across theelectrolyte to provide the carbonate ions needed for the reactionsoccurring at the anode.

Several reactions can occur within a molten carbonate fuel cell such asthe example fuel cell shown in FIG. 3. The reforming reactions can beoptional, and can be reduced or eliminated if sufficient H₂ is provideddirectly to the anode. The following reactions are based on CH₄, butsimilar reactions can occur when other fuels are used in the fuel cell.<anode reforming> CH₄+H₂O=>3H₂+CO  (1)<water gas shift> CO+H₂O=>H₂+CO₂  (2)<reforming and water gas shift combined> CH₄+2H₂O=>4H₂+CO₂  (3)<anode H₂ oxidation> H₂+CO₃ ²⁻=>H₂O+CO₂+2e ⁻  (4)<cathode> ½O₂+CO₂+2e ⁻=>CO₃ ²⁻  (5)

Reaction (1) represents the basic hydrocarbon reforming reaction togenerate H₂ for use in the anode of the fuel cell. The CO formed inreaction (1) can be converted to H₂ by the water-gas shift reaction (2).The combination of reactions (1) and (2) is shown as reaction (3).Reactions (1) and (2) can occur external to the fuel cell, and/or thereforming can be performed internal to the anode.

Reactions (4) and (5), at the anode and cathode respectively, representthe reactions that can result in electrical power generation within thefuel cell. Reaction (4) combines H₂, either present in the feed oroptionally generated by reactions (1) and/or (2), with carbonate ions toform H₂O, CO₂, and electrons to the circuit. Reaction (5) combines O₂,CO₂, and electrons from the circuit to form carbonate ions. Thecarbonate ions generated by reaction (5) can be transported across theelectrolyte of the fuel cell to provide the carbonate ions needed forreaction (4). In combination with the transport of carbonate ions acrossthe electrolyte, a closed current loop can then be formed by providingan electrical connection between the anode and cathode.

In various embodiments, a goal of operating the fuel cell can be toimprove the total efficiency of the fuel cell and/or the totalefficiency of the fuel cell plus an integrated chemical synthesisprocess. This is typically in contrast to conventional operation of afuel cell, where the goal can be to operate the fuel cell with highelectrical efficiency for using the fuel provided to the cell forgeneration of electrical power. As defined above, total fuel cellefficiency may be determined by dividing the electric output of the fuelcell plus the lower heating value of the fuel cell outputs by the lowerheating value of the input components for the fuel cell. In other words,TFCE=(LHV(el)+LHV(sg out))/LHV(in), where LHV(in) and LHV(sg out) referto the LHV of the fuel components (such as H₂, CH₄, and/or CO) deliveredto the fuel cell and syngas (H₂, CO and/or CO₂) in the anode outletstreams or flows, respectively. This can provide a measure of theelectric energy plus chemical energy generated by the fuel cell and/orthe integrated chemical process. It is noted that under this definitionof total efficiency, heat energy used within the fuel cell and/or usedwithin the integrated fuel cell/chemical synthesis system can contributeto total efficiency. However, any excess heat exchanged or otherwisewithdrawn from the fuel cell or integrated fuel cell/chemical synthesissystem is excluded from the definition. Thus, if excess heat from thefuel cell is used, for example, to generate steam for electricitygeneration by a steam turbine, such excess heat is excluded from thedefinition of total efficiency.

Several operational parameters may be manipulated to operate a fuel cellwith excess reformable fuel. Some parameters can be similar to thosecurrently recommended for fuel cell operation. In some aspects, thecathode conditions and temperature inputs to the fuel cell can besimilar to those recommended in the literature. For example, the desiredelectrical efficiency and the desired total fuel cell efficiency may beachieved at a range of fuel cell operating temperatures typical formolten carbonate fuel cells. In typical operation, the temperature canincrease across the fuel cell.

In other aspects, the operational parameters of the fuel cell candeviate from typical conditions so that the fuel cell is operated toallow a temperature decrease from the anode inlet to the anode outletand/or from the cathode inlet to the cathode outlet. For example, thereforming reaction to convert a hydrocarbon into H₂ and CO is anendothermic reaction. If a sufficient amount of reforming is performedin a fuel cell anode relative to the amount of oxidation of hydrogen togenerate electrical current, the net heat balance in the fuel cell canbe endothermic. This can cause a temperature drop between the inlets andoutlets of a fuel cell. During endothermic operation, the temperaturedrop in the fuel cell can be controlled so that the electrolyte in thefuel cell remains in a molten state.

Parameters that can be manipulated in a way so as to differ from thosecurrently recommended can include the amount of fuel provided to theanode, the composition of the fuel provided to the anode, and/or theseparation and capture of syngas in the anode output without significantrecycling of syngas from the anode exhaust to either the anode input orthe cathode input. In some aspects, no recycle of syngas or hydrogenfrom the anode exhaust to either the anode input or the cathode inputcan be allowed to occur, either directly or indirectly. In additional oralternative aspects, a limited amount of recycle can occur. In suchaspects, the amount of recycle from the anode exhaust to the anode inputand/or the cathode input can be less than about 10 vol % of the anodeexhaust, such as less than about 5 vol %, or less than about 1 vol %.

Additionally or alternately, a goal of operating a fuel cell can be toseparate CO₂ from the output stream of a combustion reaction or anotherprocess that produces a CO₂ output stream, in addition to allowinggeneration of electric power. In such aspects, the combustionreaction(s) can be used to power one or more generators or turbines,which can provide a majority of the power generated by the combinedgenerator/fuel cell system. Rather than operating the fuel cell tooptimize power generation by the fuel cell, the system can instead beoperated to improve the capture of carbon dioxide from thecombustion-powered generator while reducing or minimizing the number offuels cells required for capturing the carbon dioxide. Selecting anappropriate configuration for the input and output flows of the fuelcell, as well as selecting appropriate operating conditions for the fuelcell, can allow for a desirable combination of total efficiency andcarbon capture.

In some embodiments, the fuel cells in a fuel cell array can be arrangedso that only a single stage of fuel cells (such as fuel cell stacks) canbe present. In this type of embodiment, the anode fuel utilization forthe single stage can represent the anode fuel utilization for the array.Another option can be that a fuel cell array can contain multiple stagesof anodes and multiple stages of cathodes, with each anode stage havinga fuel utilization within the same range, such as each anode stagehaving a fuel utilization within 10% of a specified value, for examplewithin 5% of a specified value. Still another option can be that eachanode stage can have a fuel utilization equal to a specified value orlower than the specified value by less than an amount, such as havingeach anode stage be not greater than a specified value by 10% or less,for example, by 5% or less. As an illustrative example, a fuel cellarray with a plurality of anode stages can have each anode stage bewithin about 10% of 50% fuel utilization, which would correspond to eachanode stage having a fuel utilization between about 40% and about 60%.As another example, a fuel cell array with a plurality of stages canhave each anode stage be not greater than 60% anode fuel utilizationwith the maximum deviation being about 5% less, which would correspondto each anode stage having a fuel utilization between about 55% to about60%. In still another example, one or more stages of fuel cells in afuel cell array can be operated at a fuel utilization from about 30% toabout 50%, such as operating a plurality of fuel cell stages in thearray at a fuel utilization from about 30% to about 50%. More generally,any of the above types of ranges can be paired with any of the anodefuel utilization values specified herein.

Still another additional or alternate option can include specifying afuel utilization for less than all of the anode stages. For example, insome aspects of the invention fuel cells/stacks can be arranged at leastpartially in one or more series arrangements such that anode fuelutilization can be specified for the first anode stage in a series, thesecond anode stage in a series, the final anode stage in a series, orany other convenient anode stage in a series. As used herein, the“first” stage in a series corresponds to the stage (or set of stages, ifthe arrangement contains parallel stages as well) to which input isdirectly fed from the fuel source(s), with later (“second,” “third,”“final,” etc.) stages representing the stages to which the output fromone or more previous stages is fed, instead of directly from therespective fuel source(s). In situations where both output from previousstages and input directly from the fuel source(s) are co-fed into astage, there can be a “first” (set of) stage(s) and a “last” (set of)stage(s), but other stages (“second,” “third,” etc.) can be more trickyamong which to establish an order (e.g., in such cases, ordinal ordercan be determined by concentration levels of one or more components inthe composite input feed composition, such as CO₂ for instance, fromhighest concentration “first” to lowest concentration “last” withapproximately similar compositional distinctions representing the sameordinal level.)

Yet another additional or alternate option can be to specify the anodefuel utilization corresponding to a particular cathode stage (again,where fuel cells/stacks can be arranged at least partially in one ormore series arrangements). As noted above, based on the direction of theflows within the anodes and cathodes, the first cathode stage may notcorrespond to (be across the same fuel cell membrane from) the firstanode stage. Thus, in some aspects of the invention, the anode fuelutilization can be specified for the first cathode stage in a series,the second cathode stage in a series, the final cathode stage in aseries, or any other convenient cathode stage in a series.

Yet still another additional or alternate option can be to specify anoverall average of fuel utilization over all fuel cells in a fuel cellarray. In various aspects, the overall average of fuel utilization for afuel cell array can be about 65% or less, for example, about 60% orless, about 55% or less, about 50% or less, or about 45% or less(additionally or alternately, the overall average fuel utilization for afuel cell array can be at least about 25%, for example at least about30%, at least about 35%, or at least about 40%). Such an average fuelutilization need not necessarily constrain the fuel utilization in anysingle stage, so long as the array of fuel cells meets the desired fuelutilization.

Applications for CO₂ Output after Capture

In various aspects of the invention, the systems and methods describedabove can allow for production of carbon dioxide as a pressurized fluid.For example, the CO₂ generated from a cryogenic separation stage caninitially correspond to a pressurized CO₂ liquid with a purity of atleast about 90%, e.g., at least about 95%, at least about 97%, at leastabout 98%, or at least about 99%. This pressurized CO₂ stream can beused, e.g., for injection into wells in order to further enhance oil orgas recovery such as in secondary oil recovery. When done in proximityto a facility that encompasses a gas turbine, the overall system maybenefit from additional synergies in use of electrical/mechanical powerand/or through heat integration with the overall system.

Alternatively, for systems dedicated to an enhanced oil recovery (EOR)application (i.e., not comingled in a pipeline system with tightcompositional standards), the CO₂ separation requirements may besubstantially relaxed. The EOR application can be sensitive to thepresence of O₂, so O₂ can be absent, in some embodiments, from a CO₂stream intended for use in EOR. However, the EOR application can tend tohave a low sensitivity to dissolved CO, H₂, and/or CH₄. Also, pipelinesthat transport the CO₂ can be sensitive to these impurities. Thosedissolved gases can typically have only subtle impacts on thesolubilizing ability of CO₂ used for EOR. Injecting gases such as CO,H₂, and/or CH₄ as EOR gases can result in some loss of fuel valuerecovery, but such gases can be otherwise compatible with EORapplications.

Additionally or alternately, a potential use for CO₂ as a pressurizedliquid can be as a nutrient in biological processes such as algaegrowth/harvesting. The use of MCFCs for CO₂ separation can ensure thatmost biologically significant pollutants could be reduced to acceptablylow levels, resulting in a CO₂-containing stream having only minoramounts of other “contaminant” gases (such as CO, H₂, N₂, and the like,and combinations thereof) that are unlikely to substantially negativelyaffect the growth of photosynthetic organisms. This can be in starkcontrast to the output streams generated by most industrial sources,which can often contain potentially highly toxic material such as heavymetals.

In this type of aspect of the invention, the CO₂ stream generated byseparation of CO₂ in the anode loop can be used to produce biofuelsand/or chemicals, as well as precursors thereof. Further additionally oralternately, CO₂ may be produced as a dense fluid, allowing for mucheasier pumping and transport across distances, e.g., to large fields ofphotosynthetic organisms. Conventional emission sources can emit hot gascontaining modest amounts of CO₂ (e.g., about 4-15%) mixed with othergases and pollutants. These materials would normally need to be pumpedas a dilute gas to an algae pond or biofuel “farm”. By contrast, theMCFC system according to the invention can produce a concentrated CO₂stream (˜60-70% by volume on a dry basis) that can be concentratedfurther to 95%+ (for example 96%⁺, 97%⁺, 98%⁺, or 99%⁺) and easilyliquefied. This stream can then be transported easily and efficientlyover long distances at relatively low cost and effectively distributedover a wide area. In these embodiments, residual heat from thecombustion source/MCFC may be integrated into the overall system aswell.

An alternative embodiment may apply where the CO₂ source/MCFC andbiological/chemical production sites are co-located. In that case, onlyminimal compression may be necessary (i.e., to provide enough CO₂pressure to use in the biological production, e.g., from about 15 psigto about 150 psig). Several novel arrangements can be possible in such acase. Secondary reforming may optionally be applied to the anode exhaustto reduce CH₄ content, and water-gas shift may optionally additionallyor alternately be present to drive any remaining CO into CO₂ and H₂.

The components from an anode output stream and/or cathode output streamcan be used for a variety of purposes. One option can be to use theanode output as a source of hydrogen, as described above. For an MCFCintegrated with or co-located with a refinery, the hydrogen can be usedas a hydrogen source for various refinery processes, such ashydroprocessing. Another option can be to additionally or alternatelyuse hydrogen as a fuel source where the CO₂ from combustion has alreadybeen “captured.” Such hydrogen can be used in a refinery or otherindustrial setting as a fuel for a boiler, furnace, and/or fired heater,and/or the hydrogen can be used as a feed for an electric powergenerator, such as a turbine. Hydrogen from an MCFC fuel cell canfurther additionally or alternately be used as an input stream for othertypes of fuel cells that require hydrogen as an input, possiblyincluding vehicles powered by fuel cells. Still another option can be toadditionally or alternately use syngas generated as an output from anMCFC fuel cell as a fermentation input.

Another option can be to additionally or alternately use syngasgenerated from the anode output. Of course, syngas can be used as afuel, although a syngas based fuel can still lead to some CO₂ productionwhen burned as fuel. In other aspects, a syngas output stream can beused as an input for a chemical synthesis process. One option can be toadditionally or alternately use syngas for a Fischer-Tropsch typeprocess, and/or another process where larger hydrocarbon molecules areformed from the syngas input. Another option can be to additionally oralternately use syngas to form an intermediate product such as methanol.Methanol could be used as the final product, but in other aspectsmethanol generated from syngas can be used to generate larger compounds,such as gasoline, olefins, aromatics, and/or other products. It is notedthat a small amount of CO₂ can be acceptable in the syngas feed to amethanol synthesis process, and/or to a Fischer-Tropsch processutilizing a shifting catalyst. Hydroformylation is an additional oralternate example of still another synthesis process that can make useof a syngas input.

It is noted that one variation on use of an MCFC to generate syngas canbe to use MCFC fuel cells as part of a system for processing methaneand/or natural gas withdrawn by an offshore oil platform or otherproduction system that is a considerable distance from its ultimatemarket. Instead of attempting to transport the gas phase output from awell, or attempting to store the gas phase product for an extendedperiod, the gas phase output from a well can be used as the input to anMCFC fuel cell array. This can lead to a variety of benefits. First, theelectric power generated by the fuel cell array can be used as a powersource for the platform. Additionally, the syngas output from the fuelcell array can be used as an input for a Fischer-Tropsch process at theproduction site. This can allow for formation of liquid hydrocarbonproducts more easily transported by pipeline, ship, or railcar from theproduction site to, for example, an on-shore facility or a largerterminal.

Still other integration options can additionally or alternately includeusing the cathode output as a source of higher purity, heated nitrogen.The cathode input can often include a large portion of air, which meansa substantial portion of nitrogen can be included in the cathode input.The fuel cell can transport CO₂ and O₂ from the cathode across theelectrolyte to the anode, and the cathode outlet can have lowerconcentrations of CO₂ and O₂, and thus a higher concentration of N₂ thanfound in air. With subsequent removal of the residual O₂ and CO₂, thisnitrogen output can be used as an input for production of ammonia orother nitrogen-containing chemicals, such as urea, ammonium nitrate,and/or nitric acid. It is noted that urea synthesis could additionallyor alternately use CO₂ separate from the anode output as an input feed.

Integration Example—Applications for Integration with CombustionTurbines

In some aspects of the invention, a combustion source for generatingpower and exhausting a CO₂-containing exhaust can be integrated with theoperation of molten carbonate fuel cells. An example of a suitablecombustion source is a gas turbine. Preferably, the gas turbine cancombust natural gas, methane gas, or another hydrocarbon gas in acombined cycle mode integrated with steam generation and heat recoveryfor additional efficiency. Modern natural gas combined cycleefficiencies are about 60% for the largest and newest designs. Theresulting CO₂-containing exhaust gas stream can be produced at anelevated temperature compatible with the MCFC operation, such as 300°C.-700° C. and preferably 500° C.-650° C. The gas source can optionallybut preferably be cleaned of contaminants such as sulfur that can poisonthe MCFC before entering the turbine. Alternatively, the gas source canbe a coal-fired generator, wherein the exhaust gas would typically becleaned post-combustion due to the greater level of contaminants in theexhaust gas. In such an alternative, some heat exchange to/from the gasmay be necessary to enable clean-up at lower temperatures. In additionalor alternate embodiments, the source of the CO₂-containing exhaust gascan be the output from a boiler, combustor, or other heat source thatburns carbon-rich fuels. In other additional or alternate embodiments,the source of the CO₂-containing exhaust gas can be bio-produced CO₂ incombination with other sources.

For integration with a combustion source, some alternativeconfigurations for processing of a fuel cell anode can be desirable. Forexample, an alternative configuration can be to recycle at least aportion of the exhaust from a fuel cell anode to the input of a fuelcell anode. The output stream from an MCFC anode can include H₂O, CO₂,optionally CO, and optionally but typically unreacted fuel (such as H₂or CH₄) as the primary output components. Instead of using this outputstream as an external fuel stream and/or an input stream for integrationwith another process, one or more separations can be performed on theanode output stream in order to separate the CO₂ from the componentswith potential fuel value, such as H₂ or CO. The components with fuelvalue can then be recycled to the input of an anode.

This type of configuration can provide one or more benefits. First, CO₂can be separated from the anode output, such as by using a cryogenic CO₂separator. Several of the components of the anode output (H₂, CO, CH₄)are not easily condensable components, while CO₂ and H₂O can beseparated individually as condensed phases. Depending on the embodiment,at least about 90 vol % of the CO₂ in the anode output can be separatedto form a relatively high purity CO₂ output stream. Alternatively, insome aspects less CO₂ can be removed from the anode output, so thatabout 50 vol % to about 90 vol % of the CO₂ in the anode output can beseparated out, such as about 80 vol % or less or about 70 vol % or less.After separation, the remaining portion of the anode output cancorrespond primarily to components with fuel value, as well as reducedamounts of CO₂ and/or H₂O. This portion of the anode output afterseparation can be recycled for use as part of the anode input, alongwith additional fuel. In this type of configuration, even though thefuel utilization in a single pass through the MCFC(s) may be low, theunused fuel can be advantageously recycled for another pass through theanode. As a result, the single-pass fuel utilization can be at a reducedlevel, while avoiding loss (exhaust) of unburned fuel to theenvironment.

Additionally or alternatively to recycling a portion of the anodeexhaust to the anode input, another configuration option can be to use aportion of the anode exhaust as an input for a combustion reaction for aturbine or other combustion device, such as a boiler, furnace, and/orfired heater. The relative amounts of anode exhaust recycled to theanode input and/or as an input to the combustion device can be anyconvenient or desirable amount. If the anode exhaust is recycled to onlyone of the anode input and the combustion device, the amount of recyclecan be any convenient amount, such as up to 100% of the portion of theanode exhaust remaining after any separation to remove CO₂ and/or H₂O.When a portion of the anode exhaust is recycled to both the anode inputand the combustion device, the total recycled amount by definition canbe 100% or less of the remaining portion of anode exhaust. Otherwise,any convenient split of the anode exhaust can be used. In variousembodiments of the invention, the amount of recycle to the anode inputcan be at least about 10% of the anode exhaust remaining afterseparations, for example at least about 25%, at least about 40%, atleast about 50%, at least about 60%, at least about 75%, or at leastabout 90%. Additionally or alternately in those embodiments, the amountof recycle to the anode input can be about 90% or less of the anodeexhaust remaining after separations, for example about 75% or less,about 60% or less, about 50% or less, about 40% or less, about 25% orless, or about 10% or less. Further additionally or alternately, invarious embodiments of the invention, the amount of recycle to thecombustion device can be at least about 10% of the anode exhaustremaining after separations, for example at least about 25%, at leastabout 40%, at least about 50%, at least about 60%, at least about 75%,or at least about 90%. Additionally or alternately in those embodiments,the amount of recycle to the combustion device can be about 90% or lessof the anode exhaust remaining after separations, for example about 75%or less, about 60% or less, about 50% or less, about 40% or less, about25% or less, or about 10% or less.

In still other alternative aspects of the invention, the fuel for acombustion device can additionally or alternately be a fuel with anelevated quantity of components that are inert and/or otherwise act as adiluent in the fuel. CO₂ and N₂ are examples of components in a naturalgas feed that can be relatively inert during a combustion reaction. Whenthe amount of inert components in a fuel feed reaches a sufficientlevel, the performance of a turbine or other combustion source can beimpacted. The impact can be due in part to the ability of the inertcomponents to absorb heat, which can tend to quench the combustionreaction. Examples of fuel feeds with a sufficient level of inertcomponents can include fuel feeds containing at least about 20 vol %CO₂, or fuel feeds containing at least about 40 vol % N₂, or fuel feedscontaining combinations of CO₂ and N₂ that have sufficient inert heatcapacity to provide similar quenching ability. (It is noted that CO₂ hasa greater heat capacity than N₂, and therefore lower concentrations ofCO₂ can have a similar impact as higher concentrations of N₂. CO₂ canalso participate in the combustion reactions more readily than N₂, andin doing so remove H₂ from the combustion. This consumption of H₂ canhave a large impact on the combustion of the fuel, by reducing the flamespeed and narrowing the flammability range of the air and fuel mixture.)More generally, for a fuel feed containing inert components that impactthe flammability of the fuel feed, the inert components in the fuel feedcan be at least about 20 vol %, such as at least about 40 vol %, or atleast about 50 vol %, or at least about 60 vol %. Preferably, the amountof inert components in the fuel feed can be about 80 vol % or less.

When a sufficient amount of inert components are present in a fuel feed,the resulting fuel feed can be outside of the flammability window forthe fuel components of the feed. In this type of situation, addition ofH₂ from a recycled portion of the anode exhaust to the combustion zonefor the generator can expand the flammability window for the combinationof fuel feed and H₂, which can allow, for example, a fuel feedcontaining at least about 20 vol % CO₂ or at least about 40% N₂ (orother combinations of CO₂ and N₂) to be successfully combusted.

Relative to a total volume of fuel feed and H₂ delivered to a combustionzone, the amount of H₂ for expanding the flammability window can be atleast about 5 vol % of the total volume of fuel feed plus H₂, such as atleast about 10 vol %, and/or about 25 vol % or less. Another option forcharacterizing the amount of H₂ to add to expand the flammability windowcan be based on the amount of fuel components present in the fuel feedbefore H₂ addition. Fuel components can correspond to methane, naturalgas, other hydrocarbons, and/or other components conventionally viewedas fuel for a combustion-powered turbine or other generator. The amountof H₂ added to the fuel feed can correspond to at least about one thirdof the volume of fuel components (1:3 ratio of H₂:fuel component) in thefuel feed, such as at least about half of the volume of the fuelcomponents (1:2 ratio). Additionally or alternately, the amount of H₂added to the fuel feed can be roughly equal to the volume of fuelcomponents in the fuel feed (1:1 ratio) or less. For example, for a feedcontaining about 30 vol % CH₄, about 10% N₂, and about 60% CO₂, asufficient amount of anode exhaust can be added to the fuel feed toachieve about a 1:2 ratio of H₂ to CH₄. For an idealized anode exhaustthat contained only H₂, addition of H₂ to achieve a 1:2 ratio wouldresult in a feed containing about 26 vol % CH₄, 13 vol % H₂, 9 vol % N₂,and 52 vol % CO₂.

Exhaust Gas Recycle

Aside from providing exhaust gas to a fuel cell array for capture andeventual separation of the CO₂, an additional or alternate potential usefor exhaust gas can include recycle back to the combustion reaction toincrease the CO₂ content. When hydrogen is available for addition to thecombustion reaction, such as hydrogen from the anode exhaust of the fuelcell array, further benefits can be gained from using recycled exhaustgas to increase the CO₂ content within the combustion reaction.

In various aspects of the invention, the exhaust gas recycle loop of apower generation system can receive a first portion of the exhaust gasfrom combustion, while the fuel cell array can receive a second portion.The amount of exhaust gas from combustion recycled to the combustionzone of the power generation system can be any convenient amount, suchas at least about 15% (by volume), for example at least about 25%, atleast about 35%, at least about 45%, or at least about 50%. Additionallyor alternately, the amount of combustion exhaust gas recirculated to thecombustion zone can be about 65% (by volume) or less, e.g., about 60% orless, about 55% or less, about 50% or less, or about 45% or less.

In one or more aspects of the invention, a mixture of an oxidant (suchas air and/or oxygen-enriched air) and fuel can be combusted and(simultaneously) mixed with a stream of recycled exhaust gas. The streamof recycled exhaust gas, which can generally include products ofcombustion such as CO₂, can be used as a diluent to control, adjust, orotherwise moderate the temperature of combustion and of the exhaust thatcan enter the succeeding expander. As a result of using oxygen-enrichedair, the recycled exhaust gas can have an increased CO₂ content, therebyallowing the expander to operate at even higher expansion ratios for thesame inlet and discharge temperatures, thereby enabling significantlyincreased power production.

A gas turbine system can represent one example of a power generationsystem where recycled exhaust gas can be used to enhance the performanceof the system. The gas turbine system can have a first/main compressorcoupled to an expander via a shaft. The shaft can be any mechanical,electrical, or other power coupling, thereby allowing a portion of themechanical energy generated by the expander to drive the maincompressor. The gas turbine system can also include a combustion chamberconfigured to combust a mixture of a fuel and an oxidant. In variousaspects of the invention, the fuel can include any suitable hydrocarbongas/liquid, such as syngas, natural gas, methane, ethane, propane,butane, naphtha diesel, kerosene, aviation fuel, coal derived fuel,bio-fuel, oxygenated hydrocarbon feedstock, or any combinations thereof.The oxidant can, in some embodiments, be derived from a second or inletcompressor fluidly coupled to the combustion chamber and adapted tocompress a feed oxidant. In one or more embodiments of the invention,the feed oxidant can include atmospheric air and/or enriched air. Whenthe oxidant includes enriched air alone or a mixture of atmospheric airand enriched air, the enriched air can be compressed by the inletcompressor (in the mixture, either before or after being mixed with theatmospheric air). The enriched air and/or the air-enriched air mixturecan have an overall oxygen concentration of at least about 25 volume %,e.g., at least about 30 volume %, at least about 35 volume %, at leastabout 40 volume %, at least about 45 volume %, or at least about 50volume %. Additionally or alternately, the enriched air and/or theair-enriched air mixture can have an overall oxygen concentration ofabout 80 volume % or less, such as about 70 volume % or less.

The enriched air can be derived from any one or more of several sources.For example, the enriched air can be derived from such separationtechnologies as membrane separation, pressure swing adsorption,temperature swing adsorption, nitrogen plant-byproduct streams, and/orcombinations thereof. The enriched air can additionally or alternatelybe derived from an air separation unit (ASU), such as a cryogenic ASU,for producing nitrogen for pressure maintenance or other purposes. Incertain embodiments of the invention, the reject stream from such an ASUcan be rich in oxygen, having an overall oxygen content from about 50volume % to about 70 volume %, can be used as at least a portion of theenriched air and subsequently diluted, if needed, with unprocessedatmospheric air to obtain the desired oxygen concentration.

In addition to the fuel and oxidant, the combustion chamber canoptionally also receive a compressed recycle exhaust gas, such as anexhaust gas recirculation primarily having CO₂ and nitrogen components.The compressed recycle exhaust gas can be derived from the maincompressor, for instance, and adapted to help facilitate combustion ofthe oxidant and fuel, e.g., by moderating the temperature of thecombustion products. As can be appreciated, recirculating the exhaustgas can serve to increase CO₂ concentration.

An exhaust gas directed to the inlet of the expander can be generated asa product of combustion reaction. The exhaust gas can have a heightenedCO₂ content based, at least in part, on the introduction of recycledexhaust gas into the combustion reaction. As the exhaust gas expandsthrough the expander, it can generate mechanical power to drive the maincompressor, to drive an electrical generator, and/or to power otherfacilities.

The power generation system can, in many embodiments, also include anexhaust gas recirculation (EGR) system. In one or more aspects of theinvention, the EGR system can include a heat recovery steam generator(HRSG) and/or another similar device fluidly coupled to a steam gasturbine. In at least one embodiment, the combination of the HRSG and thesteam gas turbine can be characterized as a power-producing closedRankine cycle. In combination with the gas turbine system, the HRSG andthe steam gas turbine can form part of a combined-cycle power generatingplant, such as a natural gas combined-cycle (NGCC) plant. The gaseousexhaust can be introduced to the HRSG in order to generate steam and acooled exhaust gas. The HRSG can include various units for separatingand/or condensing water out of the exhaust stream, transferring heat toform steam, and/or modifying the pressure of streams to a desired level.In certain embodiments, the steam can be sent to the steam gas turbineto generate additional electrical power.

After passing through the HRSG and optional removal of at least someH₂O, the CO₂-containing exhaust stream can, in some embodiments, berecycled for use as an input to the combustion reaction. As noted above,the exhaust stream can be compressed (or decompressed) to match thedesired reaction pressure within the vessel for the combustion reaction.

Example of Integrated System

FIG. 4 schematically shows an example of an integrated system includingintroduction of both CO₂-containing recycled exhaust gas and H₂ or COfrom the fuel cell anode exhaust into the combustion reaction forpowering a turbine. In FIG. 4, the turbine can include a compressor 402,a shaft 404, an expander 406, and a combustion zone 415. An oxygensource 411 (such as air and/or oxygen-enriched air) can be combined withrecycled exhaust gas 498 and compressed in compressor 402 prior toentering combustion zone 415. A fuel 412, such as CH₄, and optionally astream containing H₂ or CO 187 can be delivered to the combustion zone.The fuel and oxidant can be reacted in zone 415 and optionally butpreferably passed through expander 406 to generate electric power. Theexhaust gas from expander 106 can be used to form two streams, e.g., aCO₂-containing stream 422 (that can be used as an input feed for fuelcell array 425) and another CO₂-containing stream 492 (that can be usedas the input for a heat recovery and steam generator system 490, whichcan, for example, enable additional electricity to be generated usingsteam turbines 494). After passing through heat recovery system 490,including optional removal of a portion of H₂O from the CO₂-containingstream, the output stream 498 can be recycled for compression incompressor 402 or a second compressor that is not shown. The proportionof the exhaust from expander 406 used for CO₂-containing stream 492 canbe determined based on the desired amount of CO₂ for addition tocombustion zone 415.

As used herein, the EGR ratio is the flow rate for the fuel cell boundportion of the exhaust gas divided by the combined flow rate for thefuel cell bound portion and the recovery bound portion, which is sent tothe heat recovery generator. For example, the EGR ratio for flows shownin FIG. 4 is the flow rate of stream 422 divided by the combined flowrate of streams 422 and 492.

The CO₂-containing stream 422 can be passed into a cathode portion (notshown) of a molten carbonate fuel cell array 425. Based on the reactionswithin fuel cell array 425, CO₂ can be separated from stream 422 andtransported to the anode portion (not shown) of the fuel cell array 425.This can result in a cathode output stream 424 depleted in CO₂. Thecathode output stream 424 can then be passed into a heat recovery (andoptional steam generator) system 450 for generation of heat exchangeand/or additional generation of electricity using steam turbines 454(which may optionally be the same as the aforementioned steam turbines494). After passing through heat recovery and steam generator system450, the resulting flue gas stream 456 can be exhausted to theenvironment and/or passed through another type of carbon capturetechnology, such as an amine scrubber.

After transport of CO₂ from the cathode side to the anode side of fuelcell array 425, the anode output 435 can optionally be passed into awater gas shift reactor 470. Water gas shift reactor 470 can be used togenerate additional H₂ and CO₂ at the expense of CO (and H₂O) present inthe anode output 435. The output from the optional water gas shiftreactor 470 can then be passed into one or more separation stages 440,such as a cold box or a cryogenic separator. This can allow forseparation of an H₂O stream 447 and CO₂ stream 449 from the remainingportion of the anode output. The remaining portion of the anode output485 can include unreacted H₂ generated by reforming but not consumed infuel cell array 425. A first portion 445 of the H₂-containing stream 485can be recycled to the input for the anode(s) in fuel cell array 425. Asecond portion 487 of stream 485 can be used as an input for combustionzone 415. A third portion 465 can be used as is for another purposeand/or treated for subsequent further use. Although FIG. 4 and thedescription herein schematically details up to three portions, it iscontemplated that only one of these three portions can be exploited,only two can be exploited, or all three can be exploited according tothe invention.

In FIG. 4, the exhaust for the exhaust gas recycle loop is provided by afirst heat recovery and steam generator system 490, while a second heatrecovery and steam generator system 450 can be used to capture excessheat from the cathode output of the fuel cell array 425. FIG. 5 shows analternative embodiment where the exhaust gas recycle loop is provided bythe same heat recovery steam generator used for processing the fuel cellarray output. In FIG. 5, recycled exhaust gas 598 is provided by heatrecovery and steam generator system 550 as a portion of the flue gasstream 556. This can eliminate the separate heat recovery and steamgenerator system associated with the turbine.

In various embodiments of the invention, the process can be approachedas starting with a combustion reaction for powering a turbine, aninternal combustion engine, or another system where heat and/or pressuregenerated by a combustion reaction can be converted into another form ofpower. The fuel for the combustion reaction can comprise or be hydrogen,a hydrocarbon, and/or any other compound containing carbon that can beoxidized (combusted) to release energy. Except for when the fuelcontains only hydrogen, the composition of the exhaust gas from thecombustion reaction can have a range of CO₂ contents, depending on thenature of the reaction (e.g., from at least about 2 vol % to about 25vol % or less). Thus, in certain embodiments where the fuel iscarbonaceous, the CO₂ content of the exhaust gas can be at least about 2vol %, for example at least about 4 vol %, at least about 5 vol %, atleast about 6 vol %, at least about 8 vol %, or at least about 10 vol %.Additionally or alternately in such carbonaceous fuel embodiments, theCO₂ content can be about 25 vol % or less, for example about 20 vol % orless, about 15 vol % or less, about 10 vol % or less, about 7 vol % orless, or about 5 vol % or less. Exhaust gases with lower relative CO₂contents (for carbonaceous fuels) can correspond to exhaust gases fromcombustion reactions on fuels such as natural gas with lean (excess air)combustion. Higher relative CO₂ content exhaust gases (for carbonaceousfuels) can correspond to optimized natural gas combustion reactions,such as those with exhaust gas recycle, and/or combustion of fuels suchas coal.

In some aspects of the invention, the fuel for the combustion reactioncan contain at least about 90 volume % of compounds containing fivecarbons or less, e.g., at least about 95 volume %. In such aspects, theCO₂ content of the exhaust gas can be at least about 4 vol %, forexample at least about 5 vol %, at least about 6 vol %, at least about 7vol %, or at least about 7.5 vol %. Additionally or alternately, the CO₂content of the exhaust gas can be about 13 vol % or less, e.g., about 12vol % or less, about 10 vol % or less, about 9 vol % or less, about 8vol % or less, about 7 vol % or less, or about 6 vol % or less. The CO₂content of the exhaust gas can represent a range of values depending onthe configuration of the combustion-powered generator. Recycle of anexhaust gas can be beneficial for achieving a CO₂ content of at leastabout 6 vol %, while addition of hydrogen to the combustion reaction canallow for further increases in CO₂ content to achieve a CO₂ content ofat least about 7.5 vol %.

Alternative Configuration—High Severity NOx Turbine

Gas turbines can be limited in their operation by several factors. Onetypical limitation can be that the maximum temperature in the combustionzone can be controlled below certain limits to achieve sufficiently lowconcentrations of nitrogen oxides (NOx) in order to satisfy regulatoryemission limits. Regulatory emission limits can require a combustionexhaust to have a NOx content of about 20 vppm or less, and possible 10vppm or less, when the combustion exhaust is allowed to exit to theenvironment.

NOx formation in natural gas-fired combustion turbines can be a functionof temperature and residence time. Reactions that result in formation ofNOx can be of reduced and/or minimal importance below a flametemperature of about 1500° F., but NOx production can increase rapidlyas the temperature increases beyond this point. In a gas turbine,initial combustion products can be mixed with extra air to cool themixture to a temperature around 1200° F., and temperature can be limitedby the metallurgy of the expander blades. Early gas turbines typicallyexecuted the combustion in diffusion flames that had stoichiometriczones with temperatures well above 1500° F., resulting in higher NOxconcentrations. More recently, the current generation of ‘Dry Low Nox’(DLN) burners can use special pre-mixed burners to burn natural gas atcooler lean (less fuel than stoichiometric) conditions. For example,more of the dilution air can be mixed in to the initial flame, and lesscan be mixed in later to bring the temperature down to the 1200° F.turbine-expander inlet temperature. The disadvantages for DLN burnerscan include poor performance at turndown, higher maintenance, narrowranges of operation, and poor fuel flexibility. The latter can be aconcern, as DLN burners can be more difficult to apply to fuels ofvarying quality (or difficult to apply at all to liquid fuels). For lowBTU fuels, such as fuels containing a high content of CO₂, DLN burnersare typically not used and instead diffusion burners can be used. Inaddition, gas turbine efficiency can be increased by using a higherturbine-expander inlet temperature. However, because there can be alimited amount of dilution air, and this amount can decrease withincreased turbine-expander inlet temperature, the DLN burner can becomeless effective at maintaining low NOx as the efficiency of the gasturbine improves.

In various aspects of the invention, a system integrating a gas turbinewith a fuel cell for carbon capture can allow use of higher combustionzone temperatures while reducing and/or minimizing additional NOxemissions, as well as enabling DLN-like NOx savings via use of turbinefuels that are not presently compatible with DLN burners. In suchaspects, the turbine can be run at higher power (i.e., highertemperature) resulting in higher NOx emissions, but also higher poweroutput and potentially higher efficiency. In some aspects of theinvention, the amount of NOx in the combustion exhaust can be at leastabout 20 vppm, such as at least about 30 vppm, or at least about 40vppm. Additionally or alternately, the amount of NOx in the combustionexhaust can be about 1000 vppm or less, such as about 500 vppm or less,or about 250 vppm or less, or about 150 vppm or less, or about 100 vppmor less. In order to reduce the NOx levels to levels required byregulation, the resulting NOx can be equilibrated via thermal NOxdestruction (reduction of NOx levels to equilibrium levels in theexhaust stream) through one of several mechanisms, such as simplethermal destruction in the gas phase; catalyzed destruction from thenickel cathode catalyst in the fuel cell array; and/or assisted thermaldestruction prior to the fuel cell by injection of small amounts ofammonia, urea, or other reductant. This can be assisted by introductionof hydrogen derived from the anode exhaust. Further reduction of NOx inthe cathode of the fuel cell can be achieved via electrochemicaldestruction wherein the NOx can react at the cathode surface and can bedestroyed. This can result in some nitrogen transport across themembrane electrolyte to the anode, where it may form ammonia or otherreduced nitrogen compounds. With respect to NOx reduction methodsinvolving an MCFC, the expected NOx reduction from a fuel cell/fuel cellarray can be about 80% or less of the NOx in the input to the fuel cellcathode, such as about 70% or less, and/or at least about 5%. It isnoted that sulfidic corrosion can also limit temperatures and affectturbine blade metallurgy in conventional systems. However, the sulfurrestrictions of the MCFC system can typically require reduced fuelsulfur levels that reduce or minimize concerns related to sulfidiccorrosion. Operating the MCFC array at low fuel utilization can furthermitigate such concerns, such as in aspects where a portion of the fuelfor the combustion reaction corresponds to hydrogen from the anodeexhaust.

ADDITIONAL EMBODIMENTS

This group of embodiments is Group A. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup.

Embodiment 1

A method for producing electricity, and hydrogen or syngas, using amolten carbonate fuel cell comprising an anode and cathode, the methodcomprising: introducing a fuel stream comprising a reformable fuel intothe anode of the molten carbonate fuel cell, an internal reformingelement associated with the anode, or a combination thereof; introducinga cathode inlet stream comprising CO₂ and O₂ into the cathode of themolten carbonate fuel cell; generating electricity within the moltencarbonate fuel cell at a fuel utilization of about 65% or less (e.g.,about 60% or less, about 55% or less, about 50% or less, about 45% orless, about 40% or less, about 35% or less, about 30% or less, about 25%or less, or about 20% or less) and at a cell operating voltage, a ratioof a cell operating voltage to a cell maximum voltage being about 0.65or less (e.g., about 0.64 or less, about 0.63 or less, about 0.62 orless, or about 0.61 or less); generating an anode exhaust from an anodeoutlet of the molten carbonate fuel cell; and separating from the anodeexhaust a H₂-containing stream, a syngas-containing stream, or acombination thereof.

Embodiment 2

The method of embodiment 1, further comprising reforming the reformablefuel, wherein at least about 90% of the reformable fuel introduced intothe anode of the molten carbonate fuel cell, the internal reformingelement associated with the anode of the molten carbonate fuel cell, orthe combination thereof, is reformed in a single pass through the anodeof the molten carbonate fuel cell.

Embodiment 3

The method of embodiment 1 or 2, wherein a reformable hydrogen contentof the reformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, is atleast about 75% greater (e.g., at least about 100% greater) than anamount of hydrogen oxidized to generate electricity.

Embodiment 4

The method of any of the above embodiments, wherein a CO₂ utilization ofthe cathode is at least about 50% (e.g., at least about 60%).

Embodiment 5

The method of any of the above embodiments, wherein the anode fuelstream comprises at least about 10 vol % inert compounds, at least about10 vol % CO₂, or a combination thereof.

Embodiment 6

The method of any of the above embodiments, wherein the anode exhaustcomprises H₂ and CO having a molar ratio of H₂ to CO from about 1.5:1 toabout 10.0:1 (e.g., from about 3.0:1 to about 10:1).

Embodiment 7

The method of any of the above embodiments, wherein the H₂-containingstream contains at least about 90% H₂ (e.g., about 95 vol % H₂, or about98 vol % H₂).

Embodiment 8

The method of any of the above embodiments, wherein the cathode inletstream comprises about 20 vol % CO₂ or less (e.g., about 15 vol % CO₂ orless, or about 12 vol % CO₂ or less).

Embodiment 9

The method of any of the above embodiments, further comprising recyclingat least a portion of the H₂-containing stream to a combustion turbine.

Embodiment 10

The method of any of the above embodiments, wherein at least about 90vol % of the reformable fuel is methane.

Embodiment 11

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a thermal ratio from about 0.25 to about 1.5(e.g., from about 0.25 to about 1.25, from about 0.25 to about 1.0, fromabout 0.25 to about 0.9, or from about 0.25 to about 0.85)

Embodiment 12

The method of any of the above embodiments, wherein a ratio of net molesof syngas in the anode exhaust to moles of CO₂ in a cathode exhaust isat least about 2.0:1 (e.g., at least about 2.5:1 or at least about 3:1).

Embodiment 13

The method of any of the above embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 45% or less, about 40% orless, about 35% or less, about 30% or less, or about 25% or less, orabout 20% or less) and a CO₂ utilization in the cathode is at leastabout 60% (e.g., at least about 65%, at least about 70%, or at leastabout 75%).

Embodiment 14

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated to generate electrical power at a current densityof at least about 150 mA/cm² and at least about 40 mW/cm² (e.g., atleast about 50 mW/cm², at least about 60 mW/cm², at least about 80mW/cm², or at least about 100 mW/cm²) of waste heat, the method furthercomprising performing an effective amount of an endothermic reaction tomaintain a temperature differential between an anode inlet and the anodeoutlet of about 100° C. or less (e.g., about 80° C. or less or about 60°C. or less), optionally wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 70%) of the waste heat.

Embodiment 15

The method of any of the above embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% and a total fuel cell efficiency for the molten carbonate fuelcell is at least about 55%.

This group of embodiments is Group B. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, the method comprising: introducing arecycled anode exhaust fuel stream, a low energy content fuel stream,and an O₂-containing stream into a combustion zone, the recycled anodeexhaust fuel stream comprising H₂, the low energy content fuel streamcomprising at least about 30 vol % of one or more inert gasses;performing a combustion reaction in the combustion zone to generate acombustion exhaust; introducing an anode fuel stream comprising areformable fuel into an anode of a molten carbonate fuel cell, aninternal reforming element associated with the anode of the moltencarbonate fuel cell, or a combination thereof; introducing a cathodeinlet stream comprising CO₂ and O₂ into a cathode of the moltencarbonate fuel cell; generating electricity within the molten carbonatefuel cell; generating an anode exhaust comprising H₂ from an anodeoutlet of the molten carbonate fuel cell; and separating at least aportion of the anode exhaust to form the recycled anode exhaust fuelstream.

Embodiment 2

The method of Embodiment 1, wherein the low energy content fuel streamcomprises at least about 35 vol %.

Embodiment 3

The method of Embodiment 1 or 2, wherein the one or more inert gases inthe low energy content fuel stream are CO₂, N₂, or a combinationthereof.

Embodiment 4

The method of any of the above Embodiments, wherein a fuel utilizationof the anode of the molten carbonate fuel cell is about 65% or less(e.g., about 60% or less).

Embodiment 5

The method of any of the above Embodiments, wherein the fuel utilizationof the anode of the molten carbonate fuel cell is about 30% to about50%.

Embodiment 6

The method of any of the above Embodiments, further comprising recyclingan anode-recycle portion of the anode exhaust stream to the one or morefuel cell anodes.

Embodiment 7

The method of any of the above Embodiments, wherein the reformable fuelcomprises CH₄.

Embodiment 8

The method of any of the above Embodiments, wherein the cathode inletstream comprises at least a portion of the combustion exhaust.

Embodiment 9

The method of any of the above Embodiments, wherein the combustionexhaust comprises about 10 vol % or less of CO₂, (e.g., about 8 vol % orless of CO₂), the combustion exhaust optionally comprising at leastabout 4 vol % of CO₂.

Embodiment 10

The method of any of the above Embodiments, wherein the anode exhauststream comprises at least about 5.0 vol % of H₂ (e.g., at least about 10vol % or at least about 15 vol %).

Embodiment 11

The method of any of the above Embodiments, further comprising exposingthe anode exhaust stream to a water gas shift catalyst prior to theseparating at least a portion of the anode exhaust stream to form therecycled anode exhaust fuel stream, a H₂ content of the shifted anodeexhaust stream being greater than a H₂ content of the anode exhauststream prior to the exposure.

Embodiment 12

The method of any of the above Embodiments, wherein the recycled anodeexhaust fuel stream is combined with the low energy content fuel streamprior to passing the recycled anode exhaust fuel stream into thecombustion zone.

Embodiment 13

The method of any of the above Embodiments, wherein a cathode exhauststream has a CO₂ content of about 2.0 vol % or less, (e.g., about 1.5vol % or less or about 1.2 vol % or less).

This group of embodiments is Group C. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for capturing carbon dioxide from a combustion source, the methodcomprising: introducing a fuel stream and an O₂-containing stream into acombustion zone; performing a combustion reaction in the combustion zoneto generate a combustion exhaust, the combustion exhaust comprising CO₂;processing a cathode inlet stream, the cathode inlet stream comprisingat least a first portion of the combustion exhaust, with a fuel cellarray of one or more molten carbonate fuel cells to form a cathodeexhaust stream from at least one cathode outlet of the fuel cell array,the one or more molten carbonate fuel cells comprising one or more fuelcell anodes and one or more fuel cell cathodes, the one or more moltencarbonate fuel cells being operatively connected to the combustion zonethrough at least one cathode inlet; reacting carbonate from the one ormore fuel cell cathodes with H₂ within the one or more fuel cell anodesto produce electricity and an anode exhaust stream from at least oneanode outlet of the fuel cell array, the anode exhaust steam comprisingCO₂ and H₂; separating CO₂ from the anode exhaust stream in one or moreseparation stages to form a CO₂-depleted anode exhaust stream; passingat least a combustion-recycle portion of the CO₂-depleted anode exhauststream to the combustion zone; and recycling at least an anode-recycleportion of the CO₂-depleted anode exhaust stream to the one or more fuelcell anodes.

Embodiment 2

The method of Embodiment 1, wherein a fuel utilization in the one ormore fuel cell anodes is about 65% or less (e.g., about 60% or less).

Embodiment 3

The method of Embodiment 2, wherein the fuel utilization in the one ormore fuel cell anodes is about 30% to about 50%.

Embodiment 4

The method of claim Embodiment 2, wherein the one or more fuel cellanodes comprise a plurality of anode stages and the one or more fuelcell cathodes comprise a plurality of cathode stages, wherein a lowutilization anode stage in the plurality of anode stages has an anodefuel utilization of 65% or less (such as about 60% or less), the lowutilization anode stage corresponding to high utilization cathode stageof the plurality of cathode stages, the high utilization cathode stagehaving a CO₂ content at a cathode inlet as high as or higher than a CO₂at a cathode inlet of any other cathode stage of the plurality ofcathode stages.

Embodiment 5

The method of Embodiment 4, wherein the fuel utilization in the lowutilization anode stage is at least about 40%, (e.g., at least about 45%or at least about 50%).

Embodiment 6

The method of Embodiment 4, wherein a fuel utilization in each anodestage of the plurality of anode stages is about 65% or less (e.g., about60% or less).

Embodiment 7

The method of any of the above embodiments, wherein thecombustion-recycle portion of the CO₂-depleted anode exhaust streamcomprises at least about 25% of the CO₂-depleted anode exhaust stream,and wherein the anode-recycle portion of the CO₂-depleted anode exhauststream comprises at least about 25% of the CO₂-depleted anode exhauststream.

Embodiment 8

The method of Embodiment 7, further comprising passing carbon-containingfuel into the one or more fuel cell anodes, the carbon-containing fueloptionally comprising CH₄.

Embodiment 9

The method of Embodiment 8, further comprising: reforming at least aportion of the carbon-containing fuel to generate H₂; and passing atleast a portion of the generated H₂ into the one or more fuel cellanodes.

Embodiment 10

The method of Embodiment 8, wherein the carbon-containing fuel is passedinto the one or more fuel cell anodes without passing thecarbon-containing fuel into a reforming stage prior to entering the oneor more fuel cell anodes.

Embodiment 11

The method of any of the above embodiments, wherein the combustionexhaust comprises about 10 vol % or less of CO₂ (e.g., 8 vol % or lessof CO₂), the combustion exhaust optionally comprising at least about 4vol % of CO₂

Embodiment 12

The method of any of the above Embodiments, further comprising recyclinga second portion of the combustion exhaust to the combustion zone, thesecond portion of the combustion exhaust optionally comprising at leastabout 6 vol % CO₂.

Embodiment 13

The method of Embodiment 12, wherein recycling the second portion of thecombustion exhaust to the combustion zone comprises: exchanging heatbetween a second portion of the combustion exhaust and an H₂O-containingstream to form steam; separating water from the second portion of thecombustion exhaust to form an H₂O-depleted combustion exhaust stream;and passing at least a portion of the H₂O-depleted combustion exhaustinto the combustion zone.

Embodiment 14

The method of any of the above embodiments, wherein the anode exhauststream, prior to the separating CO₂ from the anode exhaust stream in oneor more separation stages, comprises at least about 5.0 vol % of H₂(e.g., at least about 10 vol % or at least about 15 vol %).

Embodiment 15

The method of any of the above embodiments, further comprising exposingthe anode exhaust stream to a water gas shift catalyst to form a shiftedanode exhaust stream prior to the separating CO₂ from the anode exhauststream in one or more separation stages, a H₂ content of the shiftedanode exhaust stream after exposure to the water gas shift catalystbeing greater than a H₂ content of the anode exhaust stream prior toexposure to the water gas shift catalyst.

Embodiment 16

The method of any of the above Embodiments, wherein thecombustion-recycle portion of the CO₂-depleted anode exhaust stream iscombined with the fuel stream prior to passing the combustion-recycleportion of the CO₂-depleted anode exhaust stream to the combustion zone.

Embodiment 17

The method of any of the above embodiments, wherein a cathode exhauststream has a CO₂ content of about 2.0 vol % or less (e.g., about 1.5 vol% or less or about 1.2 vol % or less).

Embodiment 18

The method of any of the above embodiments, wherein separating CO₂ fromthe anode exhaust stream in one or more separation stages comprises:optionally separating water from the anode exhaust stream to form anoptionally H₂O-depleted anode exhaust stream; cooling the optionallyH₂O-depleted anode exhaust stream to form a condensed phase of CO₂.

This group of embodiments is Group D. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for capturing carbon dioxide from a combustion source, the methodcomprising: introducing a combustion fuel stream and an O₂-containingstream into a combustion zone; performing a combustion reaction in thecombustion zone to generate a combustion exhaust, the combustion exhaustcomprising CO₂; processing a cathode inlet stream, the cathode inletstream comprising at least a first portion of the combustion exhaust,with a fuel cell array of one or more molten carbonate fuel cells toform a cathode exhaust stream from at least one cathode outlet of thefuel cell array, the one or more molten carbonate fuel cells comprisingone or more fuel cell anodes and one or more fuel cell cathodes, the oneor more molten carbonate fuel cells being operatively connected to thecombustion zone through at least one cathode inlet; reacting carbonatefrom the one or more fuel cell cathodes with H₂ within the one or morefuel cell anodes to produce electricity and an anode exhaust stream fromat least one anode outlet of the fuel cell array, the anode exhauststeam comprising CO₂ and H₂; separating CO₂ from the anode exhauststream in one or more separation stages to form a CO₂-depleted anodeexhaust stream; and passing at least a combustion-recycle portion of theCO₂-depleted anode exhaust stream to the combustion zone.

Embodiment 2

The method of Embodiment 1, further comprising recycling ananode-recycle portion of the CO₂-depleted anode exhaust stream to theone or more fuel cell anodes.

Embodiment 3

The method of Embodiment 2, further comprising passing carbon-containingfuel into the one or more fuel cell anodes, the carbon-containing fueloptionally comprising CH₄.

Embodiment 4

The method of Embodiment 3, wherein passing carbon-containing fuel intothe one or more fuel cell anodes comprises: reforming at least a portionof the carbon-containing fuel to generate H₂; and passing at least aportion of the generated H₂ into the one or more fuel cell anodes.

Embodiment 5

The method of Embodiment 3, wherein the carbon-containing fuel is passedinto the one or more fuel cell anodes without passing thecarbon-containing fuel into a reforming stage prior to entering the oneor more fuel cell anodes.

Embodiment 6

The method of any of the above embodiments, wherein the combustionexhaust comprises about 10 vol % or less of CO₂ (e.g., 8 vol % CO₂), thecombustion exhaust optionally comprising at least about 4 vol % of CO₂

Embodiment 7

The method of any of the above embodiments, further comprising recyclinga second portion of the combustion exhaust to the combustion zone, thesecond portion of the combustion exhaust optionally comprising at leastabout 6 vol % CO₂.

Embodiment 8

The method of Embodiment 7, wherein recycling the second portion of thecombustion exhaust to the combustion zone comprises: exchanging heatbetween the second portion of the combustion exhaust and anH₂O-containing stream to form steam; separating water from the secondportion of the combustion exhaust to form an H₂O-depleted combustionexhaust stream; and passing at least a portion of the H₂O-depletedcombustion exhaust stream into the combustion zone.

Embodiment 9

The method of any of the above embodiments, wherein the anode exhauststream, prior to the separating CO₂ from the anode exhaust stream in oneor more separation stages, comprises at least about 5.0 vol % ofhydrogen (e.g., at least about 10 vol % or at least about 15 vol %).

Embodiment 10

The method of any of the above embodiments, further comprising exposingthe anode exhaust stream to a water gas shift catalyst to form a shiftedanode exhaust stream prior to the separating CO₂ from the anode exhauststream in one or more separation stages, a H₂ content of the shiftedanode exhaust stream being greater than a H₂ content of the anodeexhaust stream prior to exposure to the water gas shift catalyst.

Embodiment 11

The method of any of the above embodiments, wherein a fuel utilizationof the one or more fuel cell anodes is about 45% to about 65% (e.g.,about 60% or less).

Embodiment 12

The method of any of the above embodiments, wherein thecombustion-recycle portion of the CO₂-depleted anode exhaust stream iscombined with the combustion fuel stream prior to passing thecombustion-recycle portion of the CO₂-depleted anode exhaust stream tothe combustion zone.

Embodiment 13

The method of any of the above embodiments, wherein a cathode exhauststream has a CO₂ content of about 2.0 vol % or less (e.g., about 1.5 vol% or less or about 1.2 vol % or less).

Embodiment 14

The method of any of the above embodiments, wherein separating CO₂ fromthe anode exhaust stream in one or more separation stages comprisescooling the anode exhaust stream to form a condensed phase of CO₂.

Embodiment 15

The method of Embodiment 14, wherein separating CO₂ from the anodeexhaust stream in one or more separation stages further comprisesseparating water from the anode exhaust stream prior to forming thecondensed phase of CO₂.

Embodiment 16

Additionally or alternately to any of the above groups of embodiments, asystem for power generation, comprising: a combustion turbine includinga compressor, the compressor receiving an oxidant input and being influid communication with a combustion zone, the combustion zone furtherreceiving at least one combustion fuel input, the combustion zone beingin fluid communication with an expander having an exhaust output; anexhaust gas recirculation system providing fluid communication between afirst portion of the expander exhaust output and the combustion zone; amolten carbonate fuel cell array comprising one or more fuel cell anodesand one or more fuel cell cathodes, the molten carbonate fuel cell arrayhaving at least one cathode input, at least one cathode output, at leastone anode input, and at least one anode output, a second portion of theexpander exhaust output being in fluid communication with the at leastone cathode input; and an anode recycle loop comprising one or morecarbon dioxide separation stages for separating an anode exhaust streamto form an anode recycle loop output, a first portion of an anoderecycle loop output being provided to the combustion zone as acombustion fuel input.

Embodiment 17

The system of Embodiment 16, wherein a second portion of the anoderecycle loop output is provided to the at least one anode input.

Embodiment 18

The system of Embodiment 16 or 17, wherein the anode recycle loopfurther comprises a water gas shift reaction stage, the anode exhauststream passing through the water gas shift reaction stage prior to atleast one stage of the one or more carbon dioxide separation stages.

Embodiment 19

The system of any of Embodiments 16 to 18, wherein the exhaust gasrecirculation system further comprises a heat recovery steam generationsystem.

Embodiment 20

The system of any of Embodiments 16 to 19, wherein the exhaust gasrecirculation system provides fluid communication between a firstportion of the expander exhaust output and the combustion zone bypassing the first portion of the expander exhaust output into thecompressor.

This group of embodiments is Group E. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for capturing carbon dioxide from a combustion source, saidmethod comprising: capturing an output stream from a combustion source,the captured output stream comprising oxygen and carbon dioxide;processing the captured output stream with a fuel cell array of one ormore molten carbonate fuel cells to form a cathode exhaust stream fromat least one cathode outlet of the fuel cell array, the one or moremolten carbonate fuel cells comprising one or more fuel cell anodes andone or more fuel cell cathodes, the one or more molten carbonate fuelcells being operatively connected to the captured output stream from thecombustion source through at least one cathode inlet; reacting carbonatefrom the one or more fuel cell cathodes with H₂ within the one or morefuel cell anodes to produce electricity and an anode exhaust stream fromat least one anode outlet of the fuel cell array, the anode exhauststeam comprising CO₂ and H₂; optionally passing the anode exhaust streamthrough a water gas shift reaction stage to form an optionally shiftedanode exhaust stream; separating carbon dioxide from the optionallyshifted anode exhaust stream in one or more separation stages to form aCO₂-depleted anode exhaust stream; and recycling at least a portion ofthe CO₂-depleted anode exhaust stream to the one or more fuel cellanodes, at least a portion of the H₂ reacted with carbonate comprisingH₂ from the recycled at least a portion of the CO₂-depleted anodeexhaust stream.

Embodiment 2

The method of Embodiment 1, wherein a H₂ content of the anode exhauststream is at least about 10 vol % (e.g., at least about 20 vol %).

Embodiment 3

The method of any of the above Embodiments, wherein a fuel utilizationof the one or more fuel cell anodes is about 60% or less (e.g., about50% or less).

Embodiment 4

The method of any of the above Embodiments, wherein the fuel utilizationof the one or more fuel cell anodes is at least about 30% (e.g., atleast about 40%).

Embodiment 5

The method of any of the above Embodiments, wherein a cathode exhausthas a CO₂ content of about 2.0 vol % or less (e.g, about 1.5 vol % orless).

Embodiment 6

The method of any of the above Embodiments, further comprising passingcarbon-containing fuel into the one or more fuel cell anodes.

Embodiment 7

The method of Embodiment 6, wherein the carbon-containing fuel isreformed in at least one reforming stage internal to an assembly, theassembly comprising the at least one reforming stage and the fuel cellarray.

Embodiment 8

The method of Embodiment 6 or 7, wherein the H₂ from the recycled atleast a portion of the CO₂-depleted anode exhaust stream comprises atleast about 5 vol % of an anode input stream.

Embodiment 9

The method of Embodiment 8, wherein the carbon-containing fuel is passedinto the one or more fuel cell anodes without passing thecarbon-containing fuel into a reforming stage prior to entering the oneor more fuel cell anodes.

Embodiment 10

The method of any of Embodiments 6-9, wherein the carbon-containing fuelcomprises methane.

Embodiment 11

The method of any of the above Embodiments, wherein the at least aportion of the CO₂-depleted anode exhaust stream is recycled to the oneor more anodes without recycling a portion of the anode exhaust stream,directly or indirectly, to the one or more cathodes.

Embodiment 12

The method of any of the above Embodiments, wherein the captured outputstream comprises at least about 4 vol % CO₂.

Embodiment 13

The method of any of the above claims, wherein the captured outputstream comprises about 8 vol % CO₂ or less.

This group of embodiments is Group F. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, and hydrogen or syngas, using a moltencarbonate fuel cell comprising an anode and a cathode, the methodcomprising:

introducing an anode fuel stream comprising a reformable fuel into theanode of the molten carbonate fuel cell, an internal reforming elementassociated with the anode of the molten carbonate fuel cell, or acombination thereof; introducing a cathode inlet stream comprising CO₂and O₂ into the cathode of the molten carbonate fuel cell; generatingelectricity within the molten carbonate fuel cell; generating an anodeexhaust from an anode outlet of the molten carbonate fuel cell;separating from the anode exhaust a H₂-containing stream, asyngas-containing stream, or a combination thereof, wherein an amount ofthe reformable fuel introduced into the anode of the molten carbonatefuel cell, the internal reforming element associated with the anode ofthe molten carbonate fuel cell, or the combination thereof, provides areformable fuel surplus ratio of at least about 2.0 (e.g., at leastabout 2.5 or at least about 3.0).

Embodiment 2

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, and hydrogen or syngas, using a moltencarbonate fuel cell comprising an anode and a cathode, the methodcomprising: introducing an anode fuel stream comprising a reformablefuel into the anode of the molten carbonate fuel cell, an internalreforming element associated with the anode of the molten carbonate fuelcell, or a combination thereof; introducing a cathode inlet streamcomprising CO₂ and O₂ into the cathode of the molten carbonate fuelcell; generating electricity within the molten carbonate fuel cell;generating an anode exhaust from an anode outlet of the molten carbonatefuel cell; separating from the anode exhaust a H₂-containing stream, asyngas-containing stream, or a combination thereof, wherein the anodefuel stream has a reformable hydrogen content that is at least 50%greater than an amount of H₂ oxidized in the anode of the moltencarbonate fuel cell to generate electricity.

Embodiment 3

The method of Embodiment 1 or 2, wherein a reformable hydrogen contentof the reformable fuel introduced into the anode of the molten carbonatefuel cell, the internal reforming element associated with the anode ofthe molten carbonate fuel cell, or the combination thereof, is at leastabout 75% greater than the amount of H₂ oxidized in the anode of themolten carbonate fuel cell to generate electricity (e.g., at least about100% greater).

Embodiment 4

The method of any of the above Embodiments, the method furthercomprising reforming the reformable fuel, wherein at least about 90% ofthe reformable fuel introduced into the anode of the molten carbonatefuel cell, the internal reforming element associated with the anode ofthe molten carbonate fuel cell, or the combination thereof, is reformedin a single pass through the anode of the molten carbonate fuel cell.

Embodiment 5

The method of any of the above Embodiments, wherein a CO₂ utilization ofthe cathode is at least about 50%.

Embodiment 6

The method of any of the above Embodiments, wherein the anode fuelstream comprises at least about 10 vol % inert compounds, at least about10 vol % CO₂, or a combination thereof.

Embodiment 7

The method of any of the above Embodiments, wherein thesyngas-containing stream has a molar ratio of H₂ to CO from about 3.0:1to about 1.0:1 (e.g., from about 2.5:1 to about 1.0:1, from about 3.0:1to about 1.5:1, or from about 2.5:1 to about 1.5:1).

Embodiment 8

The method of any of the above Embodiments, wherein the anode exhausthas a molar ratio of H₂ to CO of about 1.5:1 to about 10:1 (e.g., fromabout 3.0:1 to about 10:1).

Embodiment 9

The method of any of the above Embodiments, wherein a) less than 10 vol% of the anode exhaust b) less than 10 vol % of H₂ produced in the anodeof the molten carbonate fuel cell in a single pass or c) less than 10vol % of the syngas-containing stream is directly or indirectly recycledto the anode of the molten carbonate fuel cell or the cathode of themolten carbonate fuel cell.

Embodiment 10

The method of any of Embodiments 1-8, wherein no portion of the anodeexhaust is directly or indirectly recycled to the anode of the moltencarbonate fuel cell, directly or indirectly recycled to the cathode ofthe molten carbonate fuel cell, or a combination thereof.

Embodiment 11

The method of any of the above Embodiments, further comprisingseparating at least one of CO₂ and H₂O from one or a combination of i)the anode exhaust, ii) the hydrogen-containing stream, and iii) thesyngas-containing stream.

Embodiment 12

The method of any of the above Embodiments, wherein thehydrogen-containing stream contains at least about 90 vol % H₂ (e.g.,about 95 vol % H₂, or about 98 vol % H₂).

Embodiment 13

The method of any of the above Embodiments, wherein the cathode inletstream comprises about 20 vol % CO₂ or less (e.g., about 15 vol % CO₂ orless, or about 12 vol % CO₂ or less).

Embodiment 14

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a voltage V_(A) of about 0.67 Volts or less(e.g., about 0.65 Volts or less).

This group of embodiments is Group G. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, and hydrogen or syngas, using a moltencarbonate fuel cell having an anode and cathode, the method comprising:introducing an anode fuel stream comprising a reformable fuel into theanode of the molten carbonate fuel cell, an internal reforming elementassociated with the anode of the molten carbonate fuel cell, or acombination thereof; introducing a cathode inlet stream comprising CO₂and O₂ into the cathode of the molten carbonate fuel cell; generatingelectricity within the molten carbonate fuel cell; generating an anodeexhaust from an anode outlet of the molten carbonate fuel cell;separating from the anode exhaust a hydrogen-containing stream, asyngas-containing stream, or a combination thereof, wherein anelectrical efficiency for the molten carbonate fuel cell is betweenabout 10% and about 40% and a total fuel cell efficiency for the fuelcell of at least about 55%.

Embodiment 2

The method of Embodiment 1, wherein the syngas-containing stream has amolar ratio of H₂ to CO from about 3.0:1 to about 1.0:1 (e.g., fromabout 2.5:1 to about 1.0:1, from about 3.0:1 to about 1.5:1, or fromabout 2.5:1 to about 1.5:1).

Embodiment 3

The method of any of the above Embodiments, wherein the electricalefficiency for the molten carbonate fuel cell is about 35% or less(e.g., about 30% or less, about 25% or less, or about 20% or less).

Embodiment 4

The method of any of the above Embodiments, wherein the total fuel cellefficiency for the molten carbonate fuel cell is at least about 65%(e.g., at least about 70%, at least about 75%, or at least about 80%).

Embodiment 5

The method of any of the above Embodiments, the method furthercomprising reforming the reformable fuel, wherein at least about 90% ofthe reformable fuel introduced into the anode of the molten carbonatefuel cell, the reforming stage associated with the anode of the moltencarbonate fuel cell, or a combination thereof is reformed in a singlepass through the anode of the molten carbonate fuel cell.

Embodiment 6

The method of any of the above Embodiments, wherein a reformablehydrogen content of the reformable fuel introduced into the anode of themolten carbonate fuel cell, the internal reforming element associatedwith the anode of the molten carbonate fuel cell, or the combinationthereof, is at least about 75% greater (e.g., at least about 100%greater) than an amount of H₂ oxidized in the anode of the moltencarbonate fuel cell to generate electricity.

Embodiment 7

The method of any of the above Embodiments, wherein the anode fuelstream comprises at least about 10 vol % inert compounds, at least about10 vol % CO₂, or a combination thereof.

Embodiment 8

The method of any of the above Embodiments, wherein a) less than 10 vol% of the anode exhaust, b) less than 10 vol % of H₂ produced in theanode of the molten carbonate fuel cell in a single pass, or c) lessthan 10 vol % of the syngas-containing stream is directly or indirectlyrecycled to the anode of the molten carbonate fuel cell or the cathodeof the molten carbonate fuel cell.

Embodiment 9

The method of any of Embodiments 1-7, wherein no portion of the anodeexhaust is directly or indirectly recycled to the anode of the moltencarbonate fuel cell, directly or indirectly recycled to the cathode ofthe molten carbonate fuel cell, or a combination thereof.

Embodiment 10

The method of any of the above Embodiments, further comprisingseparating at least one of CO₂ and H₂O from one or a combination of i)the anode exhaust, ii) the hydrogen-containing stream, and iii) thesyngas-containing stream.

Embodiment 11

The method of any of the above Embodiments, wherein the cathode inletstream comprises about 20 vol % CO₂ or less (e.g., about 15 vol % orless, about 12 vol % or less, or about 10 vol % or less).

Embodiment 12

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a voltage V_(A) of less than about 0.67 Voltsor less (e.g., about 0.65 Volts or less).

Embodiment 13

The method of any of the above Embodiments, wherein the anode exhausthas a molar ratio of H₂ to CO from about 1.5:1 to about 10:1 (e.g., fromabout 3.0:1 to about 10:1).

This group of embodiments is Group H. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, and hydrogen or syngas, using a moltencarbonate fuel cell, the method comprising: introducing an anode fuelstream comprising reformable fuel into an anode inlet of an anode of amolten carbonate fuel cell; introducing a cathode inlet streamcomprising CO₂ and O₂ into a cathode inlet of a cathode of the moltencarbonate fuel cell; operating the molten carbonate fuel cell togenerate electricity at a thermal ratio of about 1.3 or less (e.g.,about 1.15 or less or about 1.0 or less); generating an anode exhaustfrom an anode outlet of the molten carbonate fuel cell; and separatingfrom the anode exhaust a hydrogen-containing stream, a syngas-containingstream, or a combination thereof.

Embodiment 2

The method of Embodiment 1, wherein a CO₂ utilization of the cathode isat least about 50%.

Embodiment 3

The method of any of the above Embodiments, wherein the molten carbonatefuel cell further comprises one or more integrated endothermic reactionstages.

Embodiment 4

The method of Embodiment 3, wherein at least one integrated endothermicreaction stage of the one or more integrated endothermic reaction stagescomprises an integrated reforming stage, the anode fuel streamintroduced into the anode inlet being passed through the integratedreforming stage prior to entering the anode inlet.

Embodiment 5

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a voltage V_(A) of about 0.67 Volts or less(e.g., about 0.65 Volts or less).

Embodiment 6

The method of any of the above Embodiments, further comprisingseparating at least one of CO₂ and H₂O from one or a combination of i)the anode exhaust, ii) the hydrogen-containing stream, and iii) thesyngas-containing stream.

Embodiment 7

The method of any of the above Embodiments, wherein the thermal ratio isabout 0.85 or less, the method further comprising supplying heat to themolten carbonate fuel cell to maintain a temperature at the anode outletthat is less than a temperature at the anode inlet by about 5° C. toabout 50° C.

Embodiment 8

The method of any of the above Embodiments, wherein the thermal ratio isat least about 0.25.

Embodiment 9

The method of any of the above Embodiments, wherein a temperature at theanode outlet is greater than a temperature at the anode inlet by about40° C. or less.

Embodiment 10

The method of any of Embodiments 1-8, wherein a temperature at the anodeinlet differs from a temperature at the anode outlet by about 20° C. orless.

Embodiment 11

The method of any of Embodiments 1-8, wherein a temperature at the anodeoutlet is less than a temperature at the anode inlet by about 10° C. toabout 80° C.

Embodiment 12

The method of any of the above Embodiments, wherein a) less than 10 vol% of the anode exhaust b) less than 10 vol % of H₂ produced in the anodeof the molten carbonate fuel cell in a single pass or c) less than 10vol % of the syngas-containing stream is directly or indirectly recycledto the anode of the molten carbonate fuel cell or the cathode of themolten carbonate fuel cell.

Embodiment 13

The method of any of Embodiments 1-11, wherein no portion of the anodeexhaust is directly or indirectly recycled to the anode of the moltencarbonate fuel cell, directly or indirectly recycled to the cathode ofthe molten carbonate fuel cell, or a combination thereof.

Embodiment 14

The method of any of the above Embodiments, wherein thesyngas-containing stream has a molar ratio of H₂ to CO from about 3.0:1to about 1.0:1 (e.g., from about 2.5:1 to about 1.0:1, from about 3.0:1to about 1.5:1, or from about 2.5:1 to about 1.5:1).

Embodiment 15

The method of any of the above Embodiments, wherein the anode exhausthas a molar ratio of H₂ to CO from about 1.5:1 to about 10:1 (e.g., fromabout 3.0:1 to about 10:1).

This group of embodiments is Group J. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity using a molten carbonate fuel cellcomprising an anode and a cathode, the method comprising: introducing ananode fuel stream comprising a reformable fuel into the anode of themolten carbonate fuel cell, an internal reforming element associatedwith the anode of the molten carbonate fuel cell, or a combinationthereof; introducing a cathode inlet stream comprising CO₂ and O₂ intothe cathode of the molten carbonate fuel cell; generating electricitywithin the molten carbonate fuel cell; and generating an anode exhaustfrom an anode outlet of the molten carbonate fuel cell; wherein a ratioof net moles of syngas in the anode exhaust to moles of CO₂ in a cathodeexhaust is at least about 2.0.

Embodiment 2

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity using a molten carbonate fuel cellcomprising an anode and a cathode, the method comprising: introducing ananode fuel stream comprising a reformable fuel into the anode of themolten carbonate fuel cell, an internal reforming element associatedwith the anode of the molten carbonate fuel cell, or a combinationthereof; introducing a cathode inlet stream comprising CO₂ and O₂ intothe cathode of the molten carbonate fuel cell, a CO₂ concentration inthe cathode inlet stream being about 6 vol % or less; and generatingelectricity within the molten carbonate fuel cell; and generating ananode exhaust from an anode outlet of the molten carbonate fuel cell,wherein a ratio of net moles of syngas in the anode exhaust to moles ofCO₂ in a cathode exhaust is at least about 1.5.

Embodiment 3

The method of Embodiment 2, wherein the CO₂ concentration in the cathodeinlet stream is about 5 vol % or less.

Embodiment 4

The method of any of the above Embodiments, wherein the ratio of netmoles of syngas in the anode exhaust to moles of CO₂ in the cathodeexhaust is at least about 3.0 (e.g., at least about 4.0).

Embodiment 5

The method of any of the above Embodiments, wherein the method furthercomprises separating from the anode exhaust a H₂-containing stream, asyngas-containing stream, or a combination thereof.

Embodiment 6

The method of Embodiment 5, further comprising separating theH₂-containing stream from the anode exhaust prior to separating thesyngas-containing stream from the anode exhaust, the H₂-containingstream containing at least about 90 vol % H₂ (e.g., at least about 95vol % H₂, or at least about 98 vol % H₂).

Embodiment 7

The method of Embodiment 5 or 6, wherein the syngas-containing streamhas a molar ratio of H₂ to CO of about 3.0:1 (e.g., about 2.5:1 or less)to about 1.0:1 (e.g. at least about 1.5:1).

Embodiment 8

The method of any of Embodiments 5-7, further comprising separating atleast one of CO₂ and H₂O from one or a combination of i) the anodeexhaust, ii) the H₂-containing stream, and iii) the syngas-containingstream.

Embodiment 9

The method of any of Embodiments 5-8, further comprising separating astream containing at least about 90 vol % H₂ from the syngas-containingstream.

Embodiment 10

The method of any of the above claims, wherein the anode exhaust has aratio of H₂ to CO of about 1.5:1 (e.g., at least about 3.0:1) to about10:1.

Embodiment 11

The method of any of the above claims, wherein the anode fuel streamcomprises at least about 10 vol % inert compounds, at least about 10 vol% CO₂, or a combination thereof.

Embodiment 12

The method of any of the above claims, wherein a) less than 10 vol % ofthe anode exhaust b) less than 10 vol % of H₂ produced in the anode ofthe molten carbonate fuel cell in a single pass or c) less than 10 vol %of the syngas-containing stream is directly or indirectly recycled tothe anode of the molten carbonate fuel cell or the cathode of the moltencarbonate fuel cell.

Embodiment 13

The method of any of Embodiments 1-11, wherein no portion of the anodeexhaust is directly or indirectly recycled to the anode of the moltencarbonate fuel cell, directly or indirectly recycled to the cathode ofthe molten carbonate fuel cell, or a combination thereof.

Embodiment 14

The method of any of the above Embodiments, wherein the cathode inletstream comprises a combustion exhaust stream from a combustion-poweredgenerator.

Embodiment 15

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a voltage V_(A) of about 0.67 Volts or less.

This group of embodiments is Group K. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, and hydrogen or syngas, using a moltencarbonate fuel cell comprising an anode and a cathode, the methodcomprising: introducing an anode fuel stream comprising a reformablefuel into the anode of the molten carbonate fuel cell, an internalreforming element associated with the anode of the molten carbonate fuelcell, or a combination thereof; introducing a cathode inlet streamcomprising CO₂ and O₂ into the cathode of the molten carbonate fuelcell; generating electricity within the molten carbonate fuel cell;generating an anode exhaust from an anode outlet of the molten carbonatefuel cell; separating from the anode exhaust a H₂-containing stream, asyngas-containing stream, or a combination thereof, wherein a fuelutilization of the anode is about 50% or less and a CO₂ utilization ofthe cathode is at least about 60%.

Embodiment 2

The method of Embodiment 1, wherein a reformable hydrogen content of thereformable fuel introduced into the anode of the molten carbonate fuelcell, the internal reforming element associated with the anode of themolten carbonate fuel cell, or the combination thereof, is at leastabout 75% greater than the amount of H₂ oxidized in the anode of themolten carbonate fuel cell to generate electricity.

Embodiment 3

The method of any of the above Embodiments, wherein the cathode inletstream comprises about 20 vol % CO₂ or less (e.g., about 15 vol % CO₂ orless, or about 12 vol % CO₂ or less).

Embodiment 4

The method of any of the above Embodiments, wherein the fuel utilizationof the anode of the molten carbonate fuel cell is about 40% or less(e.g., about 30% or less).

Embodiment 5

The method of any of the above Embodiments, wherein the CO₂ utilizationof the cathode of the molten carbonate fuel cell is at least about 65%(e.g., at least about 70%).

Embodiment 6

The method of any of the above Embodiments, wherein the anode fuelstream comprises at least about 10 vol % inert compounds, at least about10 vol % CO₂, or a combination thereof.

Embodiment 7

The method of any of the above Embodiments, wherein thesyngas-containing stream has a molar ratio of H₂ to CO of about 3.0:1(e.g., about 2.5:1 or less) to about 1.0:1 (e.g., at least about 1.5:1).

Embodiment 8

The method of any of the above Embodiments, wherein the anode exhausthas a molar ratio of H₂ to CO of about 1.5:1 (e.g., at least about3.0:1) to about 10:1.

Embodiment 9

The method of any of the above Embodiments, wherein a) less than 10 vol% of the anode exhaust b) less than 10 vol % of H₂ produced in the anodeof the molten carbonate fuel cell in a single pass or c) less than 10vol % of the syngas-containing stream is directly or indirectly recycledto the anode of the molten carbonate fuel cell or the cathode of themolten carbonate fuel cell.

Embodiment 10

The method of any of Embodiments 1-8, wherein no portion of the anodeexhaust is directly or indirectly recycled to the anode of the moltencarbonate fuel cell, directly or indirectly recycled to the cathode ofthe molten carbonate fuel cell, or a combination thereof.

Embodiment 11

The method of any of the above Embodiments, further comprisingseparating at least one of CO₂ and H₂O from one or a combination of i)the anode exhaust, ii) the H₂-containing stream, and iii) thesyngas-containing stream.

Embodiment 12

The method of any of the above Embodiments, wherein the H₂-containingstream contains at least about 90 vol % H₂ (e.g., at least about 95 vol%, or at least about 98 vol %).

Embodiment 13

The method of any of the above Embodiments, wherein the cathode inletstream comprises a combustion exhaust stream from a combustion-poweredgenerator.

Embodiment 14

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a voltage V_(A) of about 0.67 Volts or less(e.g, about 0.65 Volts or less).

This group of embodiments is Group L. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for operating a molten carbonate fuel cell, the methodcomprising: introducing an anode fuel stream comprising reformable fuelinto an anode inlet of an anode of a molten carbonate fuel cell;introducing a cathode inlet stream comprising CO₂ and O₂ into a cathodeinlet of a cathode of the molten carbonate fuel cell; operating themolten carbonate fuel cell at a first operating condition to generateelectrical power and at least 30 mW/cm² of waste heat, the firstoperating condition providing a current density of at least about 150mA/cm²; generating an anode exhaust from an anode outlet of the moltencarbonate fuel cell; and performing an effective amount of anendothermic reaction to maintain a temperature differential between theanode inlet and the anode outlet of about 100° C. or less.

Embodiment 2

Additionally or alternately to any of the above groups of embodiments, amethod for operating a molten carbonate fuel cell, the methodcomprising: introducing an anode fuel stream comprising reformable fuelinto an anode inlet of an anode of a molten carbonate fuel cell;introducing a cathode inlet stream comprising CO₂ and O₂ into a cathodeinlet of a cathode of the molten carbonate fuel cell; operating themolten carbonate fuel cell at a first operating condition to generateelectricity, the first operating condition providing a current densityof at least about 150 mA/cm², the first operating condition having acorresponding baseline operating condition; generating an anode exhaustfrom an anode outlet of the molten carbonate fuel cell; and performingan effective amount of an endothermic reaction to maintain a temperaturedifferential between the anode inlet and the anode outlet of about 80°C. or less, wherein operating the molten carbonate fuel cell at thebaseline operating condition would result in a temperature increase ofat least about 100° C. between the anode inlet and the anode outlet, thebaseline operating condition for the molten carbonate fuel cell beingdefined as an operating condition that is the same as the firstoperating condition except that the baseline operating conditioncomprises a fuel utilization of the anode of the molten carbonate fuelcell of about 75% and the anode fuel stream in the baseline operatingcondition comprises at least about 80 vol % of methane.

Embodiment 3

Additionally or alternately to any of the above groups of embodiments, amethod for operating a molten carbonate fuel cell, the methodcomprising: introducing an anode fuel stream comprising reformable fuelinto an anode inlet of an anode of a molten carbonate fuel cell;introducing a cathode inlet stream comprising CO₂ and O₂ into a cathodeinlet of a cathode of the molten carbonate fuel cell; operating themolten carbonate fuel cell at a first operating condition to generateelectrical power at a first power density and waste heat, the firstoperating condition comprising a first anode inlet temperature, a firstanode inlet flow rate, a first anode fuel partial pressure, a firstanode water partial pressure, a first cathode inlet flow rate, a firstcathode inlet CO₂ partial pressure, and a first cathode inlet O₂ partialpressure, the first operating condition having a corresponding maximumpower operating condition; generating an anode exhaust from an anodeoutlet of the molten carbonate fuel cell; and performing an effectiveamount of an endothermic reaction to maintain a temperature differentialbetween the anode inlet and the anode outlet of about 80° C. or less,wherein operating the fuel cell assembly at the maximum power operatingcondition would result in a power density that differs from the firstpower density by less than about 20%, the maximum power operatingcondition corresponding to an operating condition that generates themaximum power density for an operating condition that comprises thefirst anode inlet temperature, the first anode inlet flow rate, thefirst anode fuel partial pressure, the first anode water partialpressure, the first cathode inlet flow rate, the first cathode inlet CO₂partial pressure, and the first cathode inlet O₂ partial pressure.

Embodiment 4

The method of Embodiment 3, wherein the power density at the maximumpower operating condition differs from the first power density by lessthan about 15%.

Embodiment 5

The method of any of the above Embodiments, further comprisingwithdrawing a product stream from the molten carbonate fuel cellcomprising one or more reaction products generated by performing theeffective amount of the endothermic reaction.

Embodiment 6

The method of Embodiment 5, wherein the product stream is withdrawn fromthe molten carbonate fuel cell without passing through an anode of themolten carbonate fuel cell.

Embodiment 7

The method of any of the above Embodiments, wherein the molten carbonatefuel cell further comprises one or more integrated endothermic reactionstages.

Embodiment 8

The method of Embodiment 7, wherein at least one integrated endothermicreaction stage of the one or more integrated endothermic reaction stagescomprises an integrated reforming stage, the anode fuel stream beingpassed through the integrated reforming stage prior to being introducedinto the anode inlet of the anode of the molten carbonate fuel cell.

Embodiment 9

The method of Embodiment 7 or 8, wherein performing an effective amountof an endothermic reaction comprises reforming a reformable fuel.

Embodiment 10

The method of any of the above Embodiments, wherein performing aneffective amount of an endothermic reaction comprises performing anendothermic reaction that consumes at least about 40% of the waste heatgenerated by operating the molten carbonate fuel cell at the firstoperating condition.

Embodiment 11

The method of any of the above Embodiments, wherein a temperature at theanode outlet is less than 50° C. greater than a temperature at the anodeinlet.

Embodiment 12

The method of the above Embodiments, wherein the molten carbonate fuelcell is operated to generate waste heat of at least about 40 mW/cm²(e.g., at least about 50 mW/cm², or at least about 60 mW/cm²).

Embodiment 13

The method of any of the above Embodiments, wherein the first operatingcondition provides a current density of at least about 200 mA/cm².

Embodiment 14

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a voltage V_(A) of less than about 0.7 Volts(e.g., about 0.67 Volts or less, or about 0.65 Volts or less).

Embodiment 15

The method of any of the above Embodiments, wherein no portion of theanode exhaust is directly or indirectly recycled to the anode, directlyor indirectly recycled to the cathode, or a combination thereof.

Embodiment 16

The method of any of the above Embodiments, wherein less than 10 vol %of the anode exhaust is directly or indirectly recycled to the anode ofthe molten carbonate fuel cell or the cathode of the molten carbonatefuel cell.

Embodiment 17

The method of any of the above Embodiments, further comprisingseparating from the anode exhaust a H₂-containing stream, asyngas-containing stream, or a combination thereof.

Embodiment 18

The method of Embodiment 17, wherein less than 10 vol % of H₂ producedin the anode of the molten carbonate fuel cell in a single pass isdirectly or indirectly recycled to the anode of the molten carbonatefuel cell or the cathode of the molten carbonate fuel cell.

Embodiment 19

The method of Embodiment 17, wherein less than 10 vol % of thesyngas-containing stream is directly or indirectly recycled to the anodeof the molten carbonate fuel cell or the cathode of the molten carbonatefuel cell.

This group of embodiments is Group M. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity using a molten carbonate fuel having ananode and a cathode, the method comprising: introducing a combustionfuel stream and an O₂-containing stream into a combustion zone;performing a combustion reaction in the combustion zone to generate acombustion exhaust, the combustion exhaust comprising at least about 20vppm of NOx; introducing an anode fuel stream comprising a reformablefuel into the anode of the molten carbonate fuel cell, an internalreforming element associated with the anode of the molten carbonate fuelcell, or a combination thereof; introducing a cathode inlet streamcomprising at least a portion of the combustion exhaust into the cathodeof the molten carbonate fuel cell, the cathode inlet stream comprisingCO₂, O₂, and at least about 20 vppm of a nitrogen oxide; generating a)electricity within the molten carbonate fuel cell, b) an anode exhaustcomprising H₂ and CO₂, and c) a cathode exhaust comprising less thanabout half of the NO_(x) content of the cathode inlet stream; andseparating at least a portion of the anode exhaust to form aCO₂-enriched anode exhaust stream having a higher CO₂ content than theanode exhaust and a CO₂-depleted anode exhaust stream having a lower CO₂content than the anode exhaust.

Embodiment 2

The method of embodiment 1, wherein the cathode exhaust comprises about15 vppm or less of NOx.

Embodiment 3

The method of embodiment 1 or 2, wherein the cathode inlet streamcomprises about 500 vppm or less of NOx.

Embodiment 4

The method of any of the above embodiments, wherein the combustionexhaust comprises about 10 vol % or less of CO₂ (e.g., about 8 vol % orless).

Embodiment 5

The method of any of the above embodiments, wherein the combustion zoneis operated at a temperature of at least about 1200° F.

Embodiment 6

The method of any of the above embodiments, further comprising recyclingat least a portion of the CO₂-depleted anode exhaust stream to thecombustion zone, to the anode of the molten carbonate fuel cell, or acombination thereof.

Embodiment 7

The method of any of the above embodiments, further comprising exposingthe anode exhaust stream to a water gas shift catalyst prior toseparating CO₂ from the anode exhaust stream, a H₂ content of theshifted anode exhaust stream being less than a H₂ content of the anodeexhaust stream prior to the exposure.

Embodiment 8

The method of any of the above embodiments, further comprising recyclinga combustion exhaust recycle portion from the combustion exhaust to thecombustion zone.

Embodiment 9

The method of any of the above embodiments, wherein the cathode exhauststream has a CO₂ content of about 2.0 vol. % or less (e.g., about 1.5vol % or less, or about 1.2 vol % or less).

Embodiment 10

The method of any of the above embodiments, wherein the anode fuelstream comprises at least about 10 vol % inert compounds, at least about10 vol % CO₂, or a combination thereof.

Embodiment 11

The method of any of the above embodiments, wherein the anode exhauststream comprises H₂ and CO at a molar ratio of about 3.0:1 to about10.0:1.

Embodiment 12

The method of any of the above embodiments, wherein the combustion fuelstream to the combustion zone is hydrocarbonaceous, a ratio of CO₂ inthe cathode inlet stream to NOx in the cathode inlet stream being about100 to about 10,000.

Embodiment 13

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, the method comprising: introducing oneor more fuel streams and an O₂-containing stream into a reaction zone;performing a combustion reaction in the combustion zone to generate acombustion exhaust, the combustion exhaust comprising at least about 20vppm of NOx; introducing an anode fuel stream comprising a reformablefuel into an anode of the molten carbonate fuel cell, an internalreforming element associated with the anode, or a combination thereof;introducing a cathode inlet stream comprising at least a portion of thecombustion exhaust into a cathode of the molten carbonate fuel cell, thecathode inlet stream comprising a nitrogen oxide content of about 20vppm to about 500 vppm of a nitrogen oxide; generating electricitywithin the molten carbonate fuel cell; and generating an anode exhausthaving a nitrogen oxide content that is less than half of the nitrogenoxide content of the cathode inlet stream.

Embodiment 14

The method of embodiment 13, wherein the fuel stream to the combustionzone is hydrocarbonaceous, a ratio of CO₂ in the cathode inlet stream toNOx in the cathode inlet stream being about 100 to about 10,000.

This group of embodiments is Group N. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing electricity, the method comprising: introducing afuel stream comprising a reformable fuel into an anode of a moltencarbonate fuel cell, an internal reforming element associated with theanode, or a combination thereof; introducing a cathode inlet streamcomprising CO₂ and O₂ into a cathode of the molten carbonate fuel cell;generating electricity within the molten carbonate fuel cell, the moltencarbonate fuel cell being operated at a fuel utilization of about 60% orless; generating an anode exhaust comprising H₂, CO, and CO₂;separating, from at least a portion of the anode exhaust, a firstH₂-rich gas stream comprising at least about 80 vol % (e.g., at leastabout 90%) H₂; and combusting at least a portion of the first H₂-richgas stream to produce electricity.

Embodiment 2

The method of embodiment 1, further comprising (i) performing a watergas shift process on the anode exhaust, the at least a portion of theanode exhaust, or a combination thereof; (ii) separating CO₂ and/or H₂Ofrom the anode exhaust, the at least a portion of the anode exhaust, ora combination thereof; or (iii) both (i) and (ii).

Embodiment 3

The method of embodiment 1 or 2, wherein the separating step comprises:performing a water gas shift process on the anode exhaust or at least aportion of the anode exhaust to form a shifted anode exhaust portion;and separating H₂O and CO₂ from the shifted anode exhaust portion toform the first H₂-rich gas stream.

Embodiment 4

The method of any of the above embodiments, wherein combusting stepcomprises generating steam from heat generated by the combustion, andproducing electricity from at least a portion of the generated steam.

Embodiment 5

The method of any of the above embodiments, wherein the combusting stepcomprises combusting the at least a portion of the first H₂-rich gasstream in a turbine.

Embodiment 6

The method of any of the above embodiments, wherein the cathode inletstream comprises exhaust from combustion of a carbon-containing fuel ina combustion turbine.

Embodiment 7

The method of embodiment 6, wherein the carbon-containing fuel comprisesone or more of: at least 5 vol % of inert gases; at least about 10 vol %CO₂; and at least about 10 vol % N₂.

Embodiment 8

The method of any of the above embodiments, wherein the anode exhausthas a ratio of H₂:CO of at least about 2.5:1 (e.g., at least about3.0:1, at least about 4.0:1, or at least about 5.0:1).

Embodiment 9

The method of any of the above embodiments, further comprising forming asecond H₂-containing stream from the anode exhaust, the at least aportion of the anode exhaust, the first H₂-rich gas stream, or acombination thereof; and recycling at least a portion of the secondH₂-containing stream to the combustion turbine.

Embodiment 10

The method of any of the above embodiments, wherein at least about 90vol % of the reformable fuel is methane.

Embodiment 11

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a thermal ratio from about 0.25 to about 1.5(e.g., from about 0.25 to about 1.3, from about 0.25 to about 1.15, fromabout 0.25 to about 1.0, from about 0.25 to about 0.85, from about 0.25to about 0.8, or from about 0.25 to about 0.75).

Embodiment 12

The method of any of the above embodiments, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, is atleast about 50% greater (e.g., at least about 75% greater or at leastabout 100% greater) than an amount of hydrogen reacted in the moltencarbonate fuel cell to generate electricity.

Embodiment 13

The method of any of the above embodiments, wherein a ratio of net molesof syngas in the anode exhaust to moles of CO₂ in a cathode exhaust isat least about 2.0:1 (e.g., at least about 3.0, at least about 4.0, atleast about 5.0, at least about 10.0, or at least about 20.0), andoptionally about 40.0 or less (e.g., about 30.0 or less or about 20.0 orless).

Embodiment 14

The method of any of the above embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 30% or less, about 25% orless, or about 20% or less) and a CO₂ utilization in the cathode is atleast about 60% (e.g., at least about 65%, at least about 70%, or atleast about 75%).

Embodiment 15

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated to generate electrical power at a current densityof at least about 150 mA/cm² and at least about 40 mW/cm² (e.g., atleast about 50 mW/cm², at least about 60 mW/cm², at least about 80mW/cm², or at least 100 mW/cm²) of waste heat, the method furthercomprising performing an effective amount of an endothermic reaction tomaintain a temperature differential between an anode inlet and an anodeoutlet of about 100° C. or less (e.g., about 80° C. or less or about 60°C. or less), and optionally wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 75%) of the waste heat.

Embodiment 16

The method of any of the above embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, between about 10% and about20%) and a total fuel cell efficiency for the fuel cell of at leastabout 50% (e.g., at least about 55%, at least about 60%, at least about65%, at least about 70%, at least about 75%, or at least about 80%).

This group of embodiments is Group P. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for synthesizing hydrocarbonaceous compounds, the methodcomprising: introducing a fuel stream comprising a reformable fuel intoan anode of a molten carbonate fuel cell, an internal reforming elementassociated with the anode, or a combination thereof; introducing acathode inlet stream comprising CO₂ and O₂ into a cathode inlet of themolten carbonate fuel cell; generating electricity within the moltencarbonate fuel cell; generating an anode exhaust comprising H₂, CO, H₂O,and at least about 20 vol % CO₂; reacting at least a portion of theanode exhaust under effective Fischer-Tropsch conditions in the presenceof a shifting Fischer-Tropsch catalyst (e.g., comprising Fe) to produceat least one gaseous product and at least one non-gaseous product,wherein a CO₂ concentration in the at least a portion of the anodeexhaust is at least 80% of a CO₂ concentration in the anode exhaust; andrecycling at least a portion of the at least one gaseous product to thecathode inlet.

Embodiment 2

Additionally or alternately to any of the above groups of embodiments, amethod for synthesizing hydrocarbonaceous compounds, the methodcomprising: introducing a fuel stream comprising a reformable fuel intothe anode of a molten carbonate fuel cell, an internal reforming elementassociated with a anode, or a combination thereof; introducing a cathodeinlet stream comprising CO₂ and O₂ into a cathode inlet of the moltencarbonate fuel cell; generating electricity within the molten carbonatefuel cell; generating an anode exhaust comprising H₂, CO, H₂O, and atleast about 20 vol % CO₂; and reacting at least a portion of the anodeexhaust under effective Fischer-Tropsch conditions in the presence of ashifting Fischer-Tropsch catalyst (e.g., comprising Fe) to produce atleast one gaseous product and at least one non-gaseous product, whereina CO₂ concentration in the at least a portion of the anode exhaust is atleast 80% of a CO₂ concentration in the anode exhaust, wherein an amountof the reformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, providesa reformable fuel surplus ratio of at least about 1.5.

Embodiment 3

The method of embodiment 2, further comprising recycling at least aportion of the gaseous product to the anode inlet, the cathode inlet, ora combination thereof.

Embodiment 4

The method of any of the above embodiments, wherein a ratio of H₂ to COin the anode exhaust is at least about 2.5:1 (e.g., at least about3.0:1, at least about 4.0:1, or at least about 5.0:1).

Embodiment 5

The method of any of embodiments 1 and 3-4, wherein the recycling stepcomprises: removing CO₂ from the at least one gaseous product to producea CO₂-containing stream and a separated syngas effluent comprising CO₂,CO, and H₂, such that the CO₂-containing stream has a CO₂ contentgreater than a CO₂ content in the at least one gaseous product;optionally oxidizing the at least a portion of the separated syngaseffluent; and then recycling at least a portion of the separated syngaseffluent, optionally oxidized, to the cathode inlet.

Embodiment 6

The method of any of the above embodiments, further comprisingcompressing the anode exhaust, the at least a portion of the anodeexhaust, or a combination thereof prior to the reacting of the at leasta portion of the anode exhaust under effective Fischer-Tropschconditions.

Embodiment 7

The method of any of the above embodiments, further comprising exposingat least a portion of the anode exhaust stream to a water gas shiftcatalyst to form a shifted anode exhaust, and then removing water andCO₂ from at least a portion of the shifted anode exhaust.

Embodiment 8

The method of any of the above embodiments, wherein the cathode inletstream comprises exhaust from a combustion turbine.

Embodiment 9

The method of any of the above embodiments, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, is atleast about 50% greater (e.g., at least about 75% greater or at leastabout 100% greater) than an amount of hydrogen reacted in the moltencarbonate fuel cell to generate electricity.

Embodiment 10

The method of any of the above embodiments, wherein a ratio of net molesof syngas in the anode exhaust to moles of CO₂ in a cathode exhaust isat least about 2.0:1 (e.g., at least about 3.0, at least about 4.0, atleast about 5.0, at least about 10.0, or at least about 20.0), andoptionally about 40.0 or less (e.g., about 30.0 or less or about 20.0 orless).

Embodiment 11

The method of any of the above embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 30% or less, about 25% orless, or about 20% or less) and a CO₂ utilization in a cathode is atleast about 60% (e.g., at least about 65%, at least about 70%, or atleast about 75%).

Embodiment 12

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated to generate electrical power at a current densityof at least about 150 mA/cm² and at least about 40 mW/cm² (e.g., atleast about 50 mW/cm², at least about 60 mW/cm², at least about 80mW/cm², or at least 100 mW/cm²) of waste heat, the method furthercomprising performing an effective amount of an endothermic reaction tomaintain a temperature differential between an anode inlet and an anodeoutlet of about 100° C. or less (e.g., about 80° C. or less or about 60°C. or less), and optionally wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 75%) of the waste heat.

Embodiment 13

The method of any of the above embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, between about 10% and about20%) and a total fuel cell efficiency for the fuel cell of at leastabout 50% (e.g., at least about 55%, at least about 60%, at least about65%, at least about 70%, at least about 75%, or at least about 80%).

Embodiment 14

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a thermal ratio from about 0.25 to about 1.5(e.g., from about 0.25 to about 1.3, from about 0.25 to about 1.15, fromabout 0.25 to about 1.0, from about 0.25 to about 0.85, from about 0.25to about 0.8, or from about 0.25 to about 0.75).

Embodiment 15

The method of any of the above embodiments, wherein the at least onegaseous product comprises a tail gas stream comprising one or more of(i) unreacted H₂, (ii) unreacted CO, and (iii) C4-hydrocarbonaceousand/or C4-oxygenate compounds.

This group of embodiments is Group Q. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for synthesizing hydrocarbonaceous compounds, the methodcomprising: introducing a fuel stream comprising a reformable fuel intoan anode of a molten carbonate fuel cell, an internal reforming elementassociated with the anode, or a combination thereof; introducing acathode inlet stream comprising CO₂ and O₂ into a cathode inlet of themolten carbonate fuel cell; generating electricity within the moltencarbonate fuel cell; generating an anode exhaust comprising H₂, CO, CO₂,and H₂O, and having a ratio of H₂ to CO of at least about 2.5:1 (e.g.,at least about 3.0:1, at least about 4.0:1, or at least about 5.0:1);reducing the ratio of H₂ to CO in at least a portion of the anodeexhaust to a ratio of about 1.7:1 to about 2.3:1 to form a classicsyngas stream, which also has a CO₂ concentration that is at least 60%of a CO₂ concentration in the anode exhaust; reacting the classic syngasstream under effective Fischer-Tropsch conditions in the presence of anon-shifting Fischer-Tropsch catalyst (e.g., comprising Co, Rh, Ru, Ni,Zr, or a combination thereof) to produce at least one gaseous productand at least one non-gaseous product; and recycling at least a portionof the at least one gaseous product to the cathode inlet.

Embodiment 2

Additionally or alternately to any of the above groups of embodiments, amethod for synthesizing hydrocarbonaceous compounds, the methodcomprising: introducing a fuel stream comprising a reformable fuel intoan anode of a molten carbonate fuel cell, an internal reforming elementassociated with the anode, or a combination thereof; introducing acathode inlet stream comprising CO₂ and O₂ into a cathode inlet of themolten carbonate fuel cell; generating electricity within the moltencarbonate fuel cell; generating an anode exhaust comprising H₂, CO, CO₂,and H₂O, and having a ratio of H₂ to CO of at least about 2.5:1 (e.g.,at least about 3.0:1, at least about 4.0:1, or at least about 5.0:1);reducing the ratio of H₂ to CO in at least a portion of the anodeexhaust to a ratio of about 1.7:1 to about 2.3:1 to form a classicsyngas stream, which also has a CO₂ concentration that is at least 60%of a CO₂ concentration in the anode exhaust; and reacting the classicsyngas stream under effective Fischer-Tropsch conditions in the presenceof a non-shifting Fischer-Tropsch catalyst (e.g., comprising Co, Rh, Ru,Ni, Zr, or a combination thereof) to produce at least one gaseousproduct and at least one non-gaseous product, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, providesa reformable fuel surplus ratio of at least about 1.5.

Embodiment 3

The method of embodiment 2, further comprising recycling at least aportion of the at least one gaseous product to the cathode inlet.

Embodiment 4

The method of any of the above embodiments, wherein reducing the ratioof H₂ to CO in the classic syngas stream comprises (i) performing areverse water gas shift on the classic syngas stream, (ii) withdrawing agas stream comprising H₂ from the anode exhaust, from the classic syngasstream, or from a combination thereof, or (iii) both (i) and (ii).

Embodiment 5

The method of any of embodiments 1 and 3-4, wherein the recycling stepcomprises: removing CO₂ from the at least one gaseous product to producea CO₂-containing stream and a separated syngas effluent comprising CO₂,CO, and H₂; optionally oxidizing the at least a portion of the separatedsyngas effluent; and then recycling at least a portion of the separatedsyngas effluent, optionally oxidized, to the cathode inlet.

Embodiment 6

The method of any of the above embodiments, further comprisingcompressing the anode exhaust, the classic syngas stream, or acombination thereof prior to the reacting of the classic syngas streamunder effective Fischer-Tropsch conditions.

Embodiment 7

The method of any one of the above embodiments, wherein the cathodeinlet stream comprises exhaust from a combustion turbine.

Embodiment 8

The method of any of the above embodiments, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, is atleast about 50% greater (e.g., at least about 75% greater or at leastabout 100% greater) than an amount of hydrogen reacted in the moltencarbonate fuel cell to generate electricity.

Embodiment 9

The method of any of the above embodiments, wherein a ratio of net molesof syngas in the anode exhaust to moles of CO₂ in a cathode exhaust isat least about 2.0 (e.g., at least about 3.0, at least about 4.0, atleast about 5.0, at least about 10.0, or at least about 20.0), andoptionally about 40.0 or less (e.g., about 30.0 or less or about 20.0 orless).

Embodiment 10

The method of any of the above embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 30% or less, about 25% orless, or about 20% or less) and a CO₂ utilization in a cathode is atleast about 60% (e.g., at least about 65%, at least about 70%, or atleast about 75%).

Embodiment 11

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated to generate electrical power at a current densityof at least about 150 mA/cm² and at least about 40 mW/cm² (e.g., atleast about 50 mW/cm², at least about 60 mW/cm², at least about 80mW/cm², or at least 100 mW/cm²) of waste heat, the method furthercomprising performing an effective amount of an endothermic reaction tomaintain a temperature differential between an anode inlet and an anodeoutlet of about 100° C. or less (e.g., about 80° C. or less or about 60°C. or less).

Embodiment 12

The method of embodiment 11, wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 75%) of the waste heat.

Embodiment 13

The method of any of the above embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, between about 10% and about20%) and a total fuel cell efficiency for the fuel cell of at leastabout 50% (e.g., at least about 55%, at least about 60%, at least about65%, at least about 70%, at least about 75%, or at least about 80%).

Embodiment 14

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a thermal ratio from about 0.25 to about 1.5(e.g., from about 0.25 to about 1.3, from about 0.25 to about 1.15, fromabout 0.25 to about 1.0, from about 0.25 to about 0.85, from about 0.25to about 0.8, or from about 0.25 to about 0.75).

Embodiment 15

The method of any of the above embodiments, wherein the at least onegaseous product comprises a tail gas stream comprising one or more of(i) unreacted H₂, (ii) unreacted CO, and (iii) C4-hydrocarbonaceousand/or C4-oxygenate compounds.

This group of embodiments is Group R. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for synthesizing hydrocarbonaceous compounds, the methodcomprising: introducing a fuel stream comprising a reformable fuel intoan anode of a molten carbonate fuel cell, an internal reforming elementassociated with the anode, or a combination thereof; introducing acathode inlet stream comprising CO₂ and O₂ into a cathode of the moltencarbonate fuel cell; generating electricity within the molten carbonatefuel cell; generating an anode exhaust: comprising H₂, CO, and CO₂,having a ratio of H₂ to CO of at least about 2.5:1, and having a CO₂content of at least about 20 vol %; removing water and CO₂ from at leasta portion of the anode exhaust to produce an anode effluent gas stream,the anode effluent gas stream having a concentration of water that isless than half of a concentration of water in the anode exhaust, havinga concentration of CO₂ that is less than half of a concentration of CO₂in the anode exhaust, or a combination thereof, the anode effluent gasstream also having a ratio of H₂ to CO of about 2.3:1 or less; reactingat least a portion of the anode effluent gas stream over a non-shiftingFischer-Tropsch catalyst (e.g., comprising Co, Rh, Ru, Ni, Zr, or acombination thereof) to produce at least one gaseous product and atleast one non-gaseous product; and optionally recycling at least aportion of the gaseous product to an anode inlet, to a cathode inlet, orto a combination thereof.

Embodiment 2

The method of embodiment 1, wherein the recycling step comprises:removing CO₂ from the gaseous product to produce a CO₂-concentratedstream and a separated syngas product comprising CO₂, CO, and H₂;optionally oxidizing at least a portion of the separated syngas product;and then recycling at least a portion of the separated syngas product tothe anode inlet, the cathode inlet, or a combination thereof.

Embodiment 3

The method of embodiment 1 or 2, wherein the gaseous product comprises atail gas stream comprising one or more of (i) unreacted H₂, (ii)unreacted CO, and (iii) C4-hydrocarbonaceous or C4-oxygenate compounds.

Embodiment 4

The method of any of the above embodiments, further comprising exposingat least a portion of the anode exhaust to a water gas shift catalyst toform a shifted anode exhaust (which can optionally have a molar ratio ofH₂ to CO that is less than a molar ratio of H₂ to CO in the anodeexhaust), and then removing water and CO₂ from at least a portion of theshifted anode exhaust to form a purified H₂ stream.

Embodiment 5

The method of any of the above embodiments, further comprising exposingat least a portion of the anode effluent gas stream to a water gas shiftcatalyst to form a shifted anode effluent (which can optionally have amolar ratio of H₂ to CO that is less than a molar ratio of H₂ to CO inthe anode effluent gas stream).

Embodiment 6

The method of any of the above embodiments, wherein the cathode inletstream comprises exhaust from a combustion turbine.

Embodiment 7

The method of any of the above embodiments, wherein the anode exhausthas a ratio of H₂:CO of at least about 3.0:1 (e.g., at least about4.0:1, from about 3.0:1 to about 10:1, or from about 4.0:1 to about10:1).

Embodiment 8

The method of any of the above embodiments, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, at leastabout 50% greater (e.g., at least about 75% greater or at least about100% greater) than an amount of hydrogen reacted in the molten carbonatefuel cell to generate electricity.

Embodiment 9

The method of any of the above embodiments, wherein a ratio of net molesof syngas in a fuel cell anode exhaust to moles of CO₂ in a fuel cellcathode exhaust is at least about 2.0 (e.g., at least about 3.0, atleast about 4.0, at least about 5.0, at least about 10.0, or at leastabout 20.0), and optionally about 40.0 or less (e.g., about 30.0 or lessor about 20.0 or less).

Embodiment 10

The method of any of the above embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 30% or less, about 25% orless, or about 20% or less) and a CO₂ utilization in the cathode is atleast about 60% (e.g., at least about 65%, at least about 70%, or atleast about 75%).

Embodiment 11

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated to generate electrical power at a current densityof at least about 150 mA/cm² and at least about 40 mW/cm² (e.g., atleast about 50 mW/cm², at least about 60 mW/cm², at least about 80mW/cm², or at least 100 mW/cm²) of waste heat, the method furthercomprising performing an effective amount of an endothermic reaction tomaintain a temperature differential between an anode inlet and an anodeoutlet of about 100° C. or less (e.g., about 80° C. or less or about 60°C. or less).

Embodiment 12

The method of embodiment 11, wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 75%) of the waste heat.

Embodiment 13

The method of any of the above embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, between about 10% and about20%) and a total fuel cell efficiency for the fuel cell of at leastabout 50% (e.g., at least about 55%, at least about 60%, at least about65%, at least about 70%, at least about 75%, or at least about 80%).

Embodiment 14

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a thermal ratio from about 0.25 to about 1.5(e.g., from about 0.25 to about 1.3, from about 0.25 to about 1.15, fromabout 0.25 to about 1.0, from about 0.25 to about 0.85, from about 0.25to about 0.8, or from about 0.25 to about 0.75).

Embodiment 15

The method of any of the above embodiments, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, providesa reformable fuel surplus ratio of at least about 1.5 (e.g., at leastabout 2.0, at least about 2.5, or at least about 3.0).

This group of embodiments is Group S. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for synthesizing hydrocarbonaceous compounds, the methodcomprising: introducing a fuel stream comprising a reformable fuel intoan anode of a molten carbonate fuel cell, an internal reforming elementassociated with the anode, or a combination thereof; introducing acathode inlet stream comprising CO₂ and O₂ into a cathode of the fuelcell, the cathode inlet stream optionally comprising exhaust from acombustion turbine; generating electricity within the molten carbonatefuel cell; generating an anode exhaust comprising H₂, CO, and CO₂;separating CO₂ from at least a portion of the anode exhaust to producean anode effluent gas stream; reacting at least a portion of the anodeeffluent gas stream in the presence of a methanol synthesis catalystunder effective conditions for forming methanol to produce at least onemethanol-containing stream and one or more streams comprising gaseous orliquid products; and recycling at least a portion of the one or morestreams comprising gaseous or liquid products to form at least a portionof a cathode inlet stream.

Embodiment 2

The method of embodiment 1, further comprising adjusting a compositionof the anode exhaust, the anode effluent gas stream, or a combinationthereof (e.g., by removal of CO₂ therefrom, by performing a reversewater gas shift process, or a combination thereof) to achieve a Modulevalue M for the anode effluent gas stream of about 1.7 to about 2.3(e.g., about 1.8 to about 2.3, about 1.9 to about 2.3, about 1.7 toabout 2.2, about 1.8 to about 2.2, about 1.9 to about 2.2, about 1.7 toabout 2.1, about 1.8 to about 2.1, or about 1.9 to about 2.1), where Mis defined as M=[H₂−CO₂]/[CO+CO₂].

Embodiment 3

The method of embodiment 2, wherein the adjusting step comprises:dividing the anode exhaust or the anode effluent gas stream to form afirst divided stream and a second divided stream; performing a reversewater gas shift on the first divided stream to form a first shiftedstream; and combining at least a portion of the first shifted streamwith at least a portion of the second divided stream to form an adjustedanode exhaust or an adjusted anode effluent gas stream.

Embodiment 4

The method of any of the above embodiments, wherein the anode exhausthas a molar ratio of H₂:CO of at least about 3.0:1 (e.g., at least about4.0:1 or at least about 5.0:1) and optionally of about 10:1 or less.

Embodiment 5

The method of any of the above embodiments, further comprisingcompressing the at least a portion of the anode effluent gas streamprior to the reacting in the presence of the methanol synthesiscatalyst.

Embodiment 6

The method of any of the above embodiments, wherein the one or morestreams comprising gaseous or liquid products include: (i) at least onestream comprising C2+ alcohols; (ii) at least one stream comprising H₂,CO, the reformable fuel, or a combination thereof; or (iii) both (i) and(ii).

Embodiment 7

The method of any of the above embodiments, wherein the reacting stepfurther produces at least one stream comprising syngas that is recycledfor reacting in the presence of the methanol synthesis catalyst.

Embodiment 8

The method of any of the above embodiments, wherein at least about 90vol % of the reformable fuel is methane.

Embodiment 9

The method of any of the above embodiments, wherein the fuel streamfurther comprises at least 5 vol % (e.g., at least about 10 vol %, atleast about 20 vol %, at least about 30 vol %, at least about 35 vol %,or at least about 40 vol %) of inert gases (e.g., comprising CO₂ and/orN₂).

Embodiment 10

The method of any of the above embodiments, wherein the effectivemethanol synthesis conditions comprise a pressure from about 5 MPag toabout 10 MPag and a temperature from about 250° C. to about 300° C.

Embodiment 11

The method of any of the above embodiments, further comprisingseparating H₂O from the anode exhaust, the anode effluent gas stream, ora combination thereof.

Embodiment 12

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a thermal ratio from about 0.25 to about 1.5(e.g., from about 0.25 to about 1.3, from about 0.25 to about 1.15, fromabout 0.25 to about 1.0, from about 0.25 to about 0.85, from about 0.25to about 0.8, or from about 0.25 to about 0.75).

Embodiment 13

The method of any of the above embodiments, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, providesa reformable fuel surplus ratio of at least about 1.5 (e.g., at leastabout 2.0, at least about 2.5, or at least about 3.0).

Embodiment 14

The method of any of the above embodiments, wherein a ratio of net molesof syngas in the anode exhaust to moles of CO₂ in a cathode exhaust isat least about 2.0 (e.g., at least about 3.0, at least about 4.0, atleast about 5.0, at least about 10.0, or at least about 20.0), andoptionally about 40.0 or less (e.g., about 30.0 or less or about 20.0 orless).

Embodiment 15

The method of any of the above embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 30% or less, about 25% orless, or about 20% or less) and a CO₂ utilization in the cathode is atleast about 60% (e.g., at least about 65%, at least about 70%, or atleast about 75%).

Embodiment 16

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated to generate electrical power at a current densityof at least about 150 mA/cm² and at least about 40 mW/cm² (e.g., atleast about 50 mW/cm², at least about 60 mW/cm², at least about 80mW/cm², or at least 100 mW/cm²) of waste heat, the method furthercomprising performing an effective amount of an endothermic reaction tomaintain a temperature differential between an anode inlet and an anodeoutlet of about 100° C. or less, wherein performing the endothermicreaction optionally consumes at least about 40% of the waste heat.

Embodiment 17

The method of any of the above embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, between about 10% and about20%) and a total fuel cell efficiency for the fuel cell of at leastabout 50% (e.g., at least about 55%, at least about 60%, at least about65%, at least about 70%, at least about 75%, or at least about 80%).

This group of embodiments is Group T. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for generating hydrogen in a refinery, the method comprising:introducing a fuel stream comprising a reformable fuel into an anode ofa molten carbonate fuel cell, an internal reforming element associatedwith the anode, or a combination thereof; introducing a cathode inletstream comprising CO₂ and O₂ into a cathode of the molten carbonate fuelcell; generating electricity within the molten carbonate fuel cell;generating an anode exhaust comprising H₂ and CO₂; performing aseparation (e.g., using a membrane) on the anode exhaust to form aCO₂-rich gas stream having a CO₂ content greater than a CO₂ content ofthe anode exhaust, and a CO₂-depleted gas stream having a CO₂ contentless than the CO₂ content of the anode exhaust, which CO₂-depleted gasstream optionally comprises an H₂-rich gas stream and a syngas stream;and delivering the CO₂-depleted gas stream to one or more secondrefinery processes.

Embodiment 2

The method of embodiment 1, wherein the cathode inlet stream comprisesone or more CO₂-containing streams derived directly or indirectly fromone or more first refinery processes.

Embodiment 3

The method of embodiment 1 or 2, wherein the molten carbonate fuel cellis operated at a thermal ratio from about 0.25 to about 1.5 (e.g., fromabout 0.25 to about 1.3, from about 0.25 to about 1.15, from about 0.25to about 1.0, from about 0.25 to about 0.85, or from about 0.25 to about0.75).

Embodiment 4

The method of any of the above embodiments, further comprisingseparating H₂O from at least one of the anode exhaust, the CO₂-depletedstream, and the CO₂-rich stream in one or more separation stages.

Embodiment 5

The method of any of the above embodiments, wherein an amount of thereformable fuel introduced into the anode, the internal reformingelement associated with the anode, or the combination thereof, providesa reformable fuel surplus ratio of at least about 1.5 (e.g., at leastabout 2.0, at least about 2.5 or at least about 3.0).

Embodiment 6

The method of any of the above embodiments, wherein a ratio of net molesof syngas in the anode exhaust to moles of CO₂ in a cathode exhaust isat least about 2.0 (e.g., at least about 3.0, at least about 4.0, atleast about 5.0, at least about 10.0, or at least about 20.0), andoptionally is about 40.0 or less (e.g., about 30.0 or less or about 20.0or less).

Embodiment 7

The method of any of the above embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 45% or less, about 40% orless, about 35% or less, about 30% or less, about 25% or less, or about20% or less) and a CO₂ utilization in the cathode is at least about 60%(e.g., at least about 65%, at least about 70%, or at least about 75%).

Embodiment 8

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a first operating condition to generateelectrical power and at least about 50 mW/cm² (e.g., at least about 80mW/cm² or at least 100 mW/cm²) of waste heat, the first operatingcondition providing a current density of at least about 150 mA/cm², andwherein an effective amount of an endothermic reaction is performed tomaintain a temperature differential between an anode inlet and an anodeoutlet of about 100° C. or less (e.g., about 80° C. or less or about 60°C. or less).

Embodiment 9

The method of embodiment 8, wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 75%) of the waste heat.

Embodiment 10

The method of any of the above embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, or between about 10% andabout 20%) and a total fuel cell efficiency for the molten carbonatefuel cell is at least about 55% (e.g., at least about 60%, at leastabout 65%, at least about 70%, at least about 75%, or at least about80%).

Embodiment 11

The method of any of the above embodiments, wherein one or more of thefollowing are satisfied: at least one process in the one or more firstrefinery processes is a process in the one or more second refineryprocesses; the fuel stream is derived from one or more third refineryprocesses; and the anode exhaust has a molar ratio of H₂ to CO of atleast about 3.0:1, and has a CO₂ content of at least about 10 vol %.

Embodiment 12

The method of any of the above embodiments, wherein at least a portionof the fuel stream passes through a pre-reforming stage prior to beingintroduced into the anode.

Embodiment 13

The method of any of the above embodiments, wherein at least a portionof the fuel stream passes through a desulfurization stage prior to beingintroduced into the anode.

Embodiment 14

The method of any of the above embodiments, further comprising modifyingan H₂ content of one or more of the anode exhaust, the CO₂-rich gasstream, and the a CO₂-depleted gas stream using a water gas shiftprocess.

Embodiment 15

The method of any of the above embodiments, wherein the CO₂-depleted gasstream is further separated into a first H₂-rich stream having a firstH₂ purity and a second H₂-rich stream having a second H₂ purity, whereinthe second H₂-rich stream is compressed to a pressure greater than thefirst H₂-rich stream.

This group of embodiments is Group U. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for synthesizing nitrogen-containing compounds, the methodcomprising: introducing a fuel stream comprising a reformable fuel intoan anode of a molten carbonate fuel cell, an internal reforming elementassociated with the anode, or a combination thereof; introducing acathode inlet stream comprising CO₂ and O₂ into a cathode of the fuelcell; generating electricity within the molten carbonate fuel cell;generating an anode exhaust comprising H₂ and CO₂; separating CO₂ fromat least a portion of the anode exhaust to produce a CO₂-rich streamhaving a CO₂ content greater than a CO₂ content of the anode exhaust anda CO₂-depleted gas stream having an H₂ content greater than an H₂content of the anode exhaust; and using at least a portion of theCO₂-depleted gas stream in an ammonia synthesis process and/or using atleast a portion of the CO₂-rich stream in a second synthesis process forforming an organic nitrogen-containing compound (e.g., urea).

Embodiment 2

The method of Embodiment 1, wherein using at least a portion of theCO₂-depleted gas stream comprises exposing the at least a portion of theCO₂-depleted gas stream to a catalyst under effective ammonia synthesisconditions so as to form at least one ammonia-containing stream and oneor more streams comprising gaseous or liquid products (which can includeone or more streams comprising gaseous or liquid products include atleast one stream comprising H₂ and/or CH₄), and optionally recycling atleast a portion of the one or more streams comprising gaseous or liquidproducts to form at least a portion of a cathode inlet stream.

Embodiment 3

The method of any of the above embodiments, further comprising adjustinga composition of the anode exhaust, the at least a portion of the anodeexhaust before CO₂ is separated, the CO₂-depleted gas stream, the atleast a portion of the CO₂-depleted gas stream before being used in theammonia synthesis process, or a combination thereof.

Embodiment 4

The method of Embodiment 3, wherein adjusting the composition comprisesone or more of (i) performing a water gas shift process, (ii) performinga reverse water gas shift process, (iii) performing a separation toreduce a water content of the composition, and (iv) performing aseparation to reduce a CO₂ content of the composition.

Embodiment 5

The method of any of the above embodiments, wherein the at least aportion of the CO₂-depleted gas stream is formed by separating aH₂-concentrated stream from the CO₂-depleted gas stream, the separatedH₂-concentrated stream comprising at least about 90 vol % H₂ (e.g., atleast about 95 vol % H₂, at least about 98 vol % H₂, or at least about99 vol % H₂).

Embodiment 6

The method of any of the above embodiments, wherein the anode exhausthas a molar ratio of H₂:CO of at least about 3.0:1 (e.g., at least about4.0:1), and optionally also about 10:1 or less.

Embodiment 7

The method of any of the above embodiments, further comprising:withdrawing, from a cathode exhaust, a gas stream comprising N₂; andusing at least a portion of the withdrawn gas stream comprising N₂ as asource of N₂ in an ammonia synthesis process.

Embodiment 8

The method of any of the above embodiments, wherein the second synthesisprocess further comprises using ammonia from the ammonia synthesisprocess to form the organic nitrogen-containing compound.

Embodiment 9

The method of any of the above embodiments, wherein at least about 90vol % of the reformable fuel is methane.

Embodiment 10

The method of any of the above embodiments, wherein the effectiveammonia synthesis conditions comprise a pressure from about 6 MPag toabout 18 MPag and a temperature from about 350° C. to about 500° C.

Embodiment 11

The method of any of the above claims, wherein a cathode inlet streamcomprises exhaust from a combustion turbine.

Embodiment 12

The method of any of the above embodiments, wherein at least a portionof the O₂ in the cathode inlet stream is derived from an air separationstep in which air is passed through a PSA apparatus to generate anitrogen-rich product stream and an oxygen-rich off-gas stream, suchthat at least a portion of said oxygen-rich off-gas stream is sent tothe cathode inlet, and such that at least a portion of saidnitrogen-rich product stream is sent to the ammonia synthesis process.

Embodiment 13

The method of any of the above embodiments, further comprisingwithdrawing, from a cathode exhaust, an N₂-rich gas stream comprisingN₂; and using at least a portion of the N₂-rich gas stream as a sourceof N₂ in the ammonia synthesis process (e.g., by exposing the at least aportion of the N₂-rich gas stream to a synthesis catalyst undereffective synthesis conditions).

Embodiment 14

The method of Embodiment 13, wherein using at least a portion of thecathode exhaust stream as a source of N₂ in an ammonia synthesis processcomprises performing at least one of a separation process and apurification process on the N₂-rich gas stream to increase theconcentration of N₂, and then passing at least a portion of the N₂-richgas stream into the ammonia synthesis process with the increased N₂concentration.

Embodiment 15

The method of any of the above Embodiments, further comprisingseparating H₂O from at least one of the anode exhaust, the CO₂-rich gasstream, the CO₂-depleted gas stream, and a cathode exhaust.

Embodiment 16

The method of any of the above Embodiments, further comprising exposingone or more of the CO₂-rich stream, the CO₂-depleted stream, and atleast a portion of the anode exhaust stream to a water gas shiftcatalyst.

Embodiment 17

The method of any of the above Embodiments, wherein the cathode inletstream comprises exhaust from a combustion turbine.

Embodiment 18

The method of any of the above Embodiments, wherein less than 10 vol %of an anode exhaust is directly or indirectly recycled to the anode orto the cathode.

Embodiment 19

The method of any of the above Embodiments, wherein no portion of theanode exhaust is directly or indirectly recycled to the anode.

Embodiment 20

The method of any of the above Embodiments, wherein no portion of theanode exhaust is directly or indirectly recycled to the cathode.

Embodiment 21

The method of any of the above Embodiments, wherein less than 10 vol %of H₂ produced in the anode in a single pass is directly or indirectlyrecycled to the anode or to the cathode.

Embodiment 22

The method of any of the above Embodiments, the method furthercomprising reforming the reformable fuel, wherein at least about 90% ofthe reformable fuel introduced into the anode, the reforming stageassociated with the anode, or a combination thereof is reformed in asingle pass through the anode.

Embodiment 23

The method of any of the above Embodiments, wherein a reformablehydrogen content of the reformable fuel introduced into the anode, intothe reforming stage associated with the anode, or into a combinationthereof is at least about 50% (e.g., at least about 75% or at leastabout 100%) greater than an amount of hydrogen reacted to generateelectricity.

Embodiment 24

The method of any of the above Embodiments, wherein a reformable fuelsurplus ratio is at least about 2.0 (e.g., at least about 2.5 or atleast about 3.0).

Embodiment 25

The method of any of the above Embodiments, wherein a CO₂ utilization inthe cathode is at least about 50% (e.g., at least about 60%).

Embodiment 26

The method of any of the above Embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, or between about 10% andabout 20%) and a total fuel cell efficiency for the molten carbonatefuel cell is at least about 55% (e.g., at least about 60%, at leastabout 65%, at least about 70%, at least about 75%, or at least about80%).

Embodiment 27

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a thermal ratio from about 0.25 to about 1.5(e.g., from about 0.25 to about 1.3, from about 0.25 to about 1.15, fromabout 0.25 to about 1.0, from about 0.25 to about 0.85, or from about0.25 to about 0.75).

Embodiment 28

The method of any of the above Embodiments, wherein a ratio of net molesof syngas in the anode exhaust to moles of CO₂ in a cathode exhaust isat least about 2.0 (e.g., at least about 3.0, at least about 4.0, atleast about 5.0, at least about 10.0, or at least about 20.0), andoptionally is about 40.0 or less (e.g., about 30.0 or less or about 20.0or less).

Embodiment 29

The method of any of the above Embodiments, wherein a fuel utilizationin the anode is about 50% or less (e.g., about 45% or less, about 40% orless, about 35% or less, about 30% or less, about 25% or less, or about20% or less) and a CO₂ utilization in the cathode is at least about 60%(e.g., at least about 65%, at least about 70%, or at least about 75%).

Embodiment 30

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a first operating condition to generateelectrical power and at least about 50 mW/cm² (e.g., at least 100mW/cm²) of waste heat, the first operating condition providing a currentdensity of at least about 150 mA/cm², and wherein an effective amount ofan endothermic reaction is performed to maintain a temperaturedifferential between an anode inlet and an anode outlet of about 100° C.or less (e.g., about 80° C. or less or about 60° C. or less).

Embodiment 31

The method of embodiment 30, wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 75%) of the waste heat.

This group of embodiments is Group V. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing iron and/or steel, the method comprising:introducing a fuel stream comprising a reformable fuel into an anode ofa molten carbonate fuel cell, an internal reforming element associatedwith the anode, or a combination thereof; introducing a cathode inletstream comprising CO₂ and O₂ into a cathode of the molten carbonate fuelcell; generating electricity within the molten carbonate fuel cell;withdrawing, from an anode exhaust, a first gas stream comprising CO,the anode exhaust having a pressure of about 500 kPag or less; andintroducing the first gas stream withdrawn from the anode exhaust into aprocess for production of iron and/or steel.

Embodiment 2

The method of Embodiment 1, further comprising using the electricitygenerated to provide heat to the process for production of iron and/orsteel.

Embodiment 3

The method of any of the above embodiments, further comprisingwithdrawing a second gas stream comprising H₂ from the anode exhaust,and using the second gas stream as fuel for heating the process forproduction of iron and/or steel.

Embodiment 4

The method of any of the above embodiments, further comprisingseparating water from the anode exhaust, the first gas stream withdrawnfrom the anode exhaust, or a combination thereof, and washing a processslag using the separated water.

Embodiment 5

The method of any of the above embodiments, wherein the cathode inletstream comprises at least a portion of a CO₂-containing exhaust producedby the process for production of iron and/or steel.

Embodiment 6

The method of Embodiment 5, further comprising separating CO₂ from theCO₂-containing exhaust produced by the process for production of ironand/or steel.

Embodiment 7

The method of any of the above embodiments, further comprising exposingthe first withdrawn gas stream to a water gas shift catalyst undereffective water gas shift conditions prior to introducing the withdrawnfirst gas stream into the process for production of iron and/or steel.

Embodiment 8

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated to generate electricity at a thermal ratio ofabout 1.0 or less, the method further comprising transferring heat fromthe process for production of iron and/or steel (e.g., from a furnace)to the molten carbonate fuel cell, wherein a temperature of the anodeexhaust is greater than a temperature at an anode inlet.

Embodiment 9

The method of Embodiment 8, wherein transferring heat comprisesperforming heat exchange between the anode inlet stream and at least oneof an iron and/or steel production process furnace and an iron and/orsteel production process exhaust, wherein performing the heat exchangeoptionally comprises increasing a temperature of the anode inlet streamby at least about 100° C. (e.g., by at least about 150° C.

Embodiment 10

The method of any of the above Embodiments, further comprising exposingthe withdrawn gas stream to a water gas shift catalyst under effectivewater gas shift conditions prior to introducing the gas stream into theprocess for production of iron and/or steel.

Embodiment 11

The method of any of the above embodiments, further comprisingseparating water from the anode exhaust, the withdrawn first gas stream,or a combination thereof, and washing a process slag using the separatedwater.

Embodiment 12

The method of any of the previous embodiments, wherein an amount of thereformable fuel introduced into the anode, into the internal reformingelement associated with the anode, or into the combination thereof,provides a reformable fuel surplus ratio of at least about 1.5 (e.g., atleast about 2.0, at least about 2.5, or at least about 3.0).

Embodiment 13

The method of any of the above Embodiments, the method furthercomprising reforming the reformable fuel, wherein at least about 90% ofthe reformable fuel introduced into the anode, the reforming stageassociated with the anode, or a combination thereof is reformed in asingle pass through the anode.

Embodiment 14

The method of any of the above embodiments, wherein a ratio of net molesof syngas in a fuel cell anode exhaust to moles of CO₂ in a fuel cellcathode exhaust is at least about 2.0 (e.g., at least about 3.0, atleast about 4.0, at least about 5.0, at least about 10.0, or at leastabout 20.0), and optionally about 40.0 or less (e.g., about 30.0 or lessor about 20.0 or less).

Embodiment 15

The method of any of the above Embodiments, wherein a fuel utilizationin the anode is about 65% or less (e.g., about 60% or less, about 50% orless, about 40% or less, about 30% or less, about 25% or less, or about20% or less) and a CO₂ utilization in the cathode is at least about 50%(e.g., at least about 60%, at least about 65%, at least about 70%, or atleast about 75%).

Embodiment 16

The method of any of the above Embodiments, wherein an electricalefficiency for the molten carbonate fuel cell is between about 10% andabout 40% (e.g., between about 10% and about 35%, between about 10% andabout 30%, between about 10% and about 25%, between about 10% and about20%) and a total fuel cell efficiency for the fuel cell of at leastabout 50% (e.g., at least about 55%, at least about 60%, at least about65%, at least about 70%, at least about 75%, or at least about 80%).

Embodiment 17

The method of any of the above embodiments, wherein the anode exhausthas a molar ratio of H₂:CO of at least about 3.0:1 (e.g., at least about4.0:1, from about 3.0:1 to about 10:1, or from about 4.0:1 to about10:1).

Embodiment 18

The method of any of the above embodiments, wherein at least about 90vol % of the reformable fuel is methane.

Embodiment 19

The method of any of the above Embodiments, wherein less than 10 vol %of H₂ produced in the anode in a single pass is directly or indirectlyrecycled to the anode or to the cathode.

Embodiment 20

The method of any of the above Embodiments, wherein a reformablehydrogen content of the reformable fuel introduced into the anode, areforming stage associated with the anode, or a combination thereof isat least about 50% greater (e.g., at least about 75% greater or at leastabout 100% greater) than an amount of hydrogen reacted to generateelectricity.

Embodiment 21

The method of any of the above embodiments, wherein the molten carbonatefuel cell further comprises one or more integrated endothermic reactionstages.

Embodiment 22

The method of Embodiment 21, wherein at least one of the integratedendothermic reaction stages comprises an integrated reforming stage, thefuel stream introduced into the anode optionally being passed through atleast one of the integrated reforming stages prior to entering theanode.

Embodiment 23

The method of any of the above Embodiments, wherein the molten carbonatefuel cell is operated at a first operating condition to generateelectrical power and at least about 30 mW/cm² (e.g., at least about 40mW/cm², at least about 50 mW/cm², or at least 100 mW/cm²) of waste heat,the first operating condition providing a current density of at leastabout 150 mA/cm², and wherein an effective amount of an endothermicreaction is performed to maintain a temperature differential between ananode inlet and an anode outlet of about 100° C. or less (e.g., about80° C. or less or about 60° C. or less).

Embodiment 24

The method of embodiment 23, wherein performing the endothermic reactionconsumes at least about 40% (e.g., at least about 50%, at least about60%, or at least about 75%) of the waste heat.

Embodiment 25

The method of any of the above embodiments, wherein the molten carbonatefuel cell is operated at a voltage V_(A) of less than about 0.68V (e.g.,less than about 0.67V, less than about 0.66V, or about 0.65V or less),and optionally of at least about 0.60V (e.g., at least about 0.61V, atleast about 0.62V, or at least about 0.63V).

Embodiment 26

The method of any of the above Embodiments, further comprising reformingthe reformable fuel, wherein at least about 90% of the reformable fuelintroduced into the anode, the reforming stage associated with theanode, or a combination thereof is reformed in a single pass through theanode.

This group of embodiments is Group W. References to “any of the aboveembodiments” are meant to refer only to other embodiments within thisGroup, whereas references to “any of the above groups of embodiments”are meant to refer to any individual or combination of embodiments fromone or more other Groups.

Embodiment 1

Additionally or alternately to any of the above groups of embodiments, amethod for producing a fermented product, the method comprising:introducing a fuel stream comprising a reformable fuel into an anode ofa molten carbonate fuel cell, an internal reforming element associatedwith the anode, or a combination thereof; introducing a cathode inletstream comprising CO₂ and O₂ into a cathode of the fuel cell; generatingelectricity within the molten carbonate fuel cell; separating from theanode exhaust an H₂-containing stream, a syngas-containing stream, or acombination thereof; processing biomass to produce at least onefermentation product and a fermentation exhaust; and distilling the atleast one fermentation product, at least some heat for distillationbeing provided by heat exchange with the anode exhaust, combustion ofthe syngas-containing stream, combustion of the H₂-containing stream,electric heating using the electricity generated within the moltencarbonate fuel cell, or a combination thereof, wherein the methodfurther comprises one or more of the following: a) the cathode inletstream comprises at least a portion of the fermentation exhaust; b) theprocessing step is done in the presence of H₂O separated from the anodeexhaust, H₂O separated from the syngas-containing stream, H₂O separatedfrom the H₂-containing stream, or a combination thereof; c) thereformable fuel comprises a portion of the fermentation product, thereformable fuel optionally containing at least 50 vol % of thefermentation product (e.g., at least 60 vol % or at least 70 vol %), theportion of the fermentation product optionally being a distilled portionof the fermentation product having a water to carbon ratio of about1.5:1 to about 3.0:1 (e.g., about 1.5:1 to about 2.5:1); d) theprocessing step comprises separating a substantially fermentable biomassportion from a substantially non-fermentable biomass portion, thesubstantially non-fermentable biomass portion being processed in one ormore thermal, chemical, and/or thermochemical processes in the presenceof at least a portion of the H₂-containing gas stream, at least aportion of the syngas-containing stream, or a combination thereof; e) anamount of the reformable fuel introduced into the anode of the moltencarbonate fuel cell, the internal reforming element associated with theanode of the molten carbonate fuel cell, or the combination thereof,provides a reformable fuel surplus ratio of at least about 2.0; f) areformable hydrogen content of reformable fuel introduced into the anodeof the molten carbonate fuel cell, the internal reforming elementassociated with the anode of the molten carbonate fuel cell, or thecombination thereof, is at least about 50% greater than an amount ofhydrogen oxidized to generate electricity (e.g., at least about 75%greater or at least about 100% greater); g) an electrical efficiency forthe molten carbonate fuel cell is between about 10% and about 40% (e.g.,from about 10% to about 35%, from about 10% to about 30%, or from about10% to about 25%), and a total fuel cell efficiency for the fuel cell isat least about 55% (e.g., at least about 65%, at least about 70%, atleast about 75%, or at least about 80%); h) the molten carbonate fuelcell is operated at a thermal ratio of about 0.25 to about 1.5 (e.g.,from about 0.25 to about 1.3, from about 0.25 to about 1.15, from about0.25 to about 1.0, from about 0.25 to about 0.85, or from about 0.25 toabout 0.75); i) a ratio of net moles of syngas in the anode exhaust tomoles of CO₂ in a cathode exhaust is at least about 2.0 (e.g., at leastabout 3.0, at least about 4.0, at least about 5.0, at least about 10.0,or at least about 20.0), and optionally about 40.0 or less (e.g., about30.0 or less or about 20.0 or less); j) a fuel utilization in the anodeof the molten carbonate fuel cell is about 50% or less (e.g., about 40%or less, about 30% or less, about 25% or less, or about 20% or less) anda CO₂ utilization in the cathode is at least about 60% (e.g., at leastabout 65%, at least about 70%, or at least about 75%); k) the moltencarbonate fuel cell is operated at a first operating condition togenerate electrical power and at least 100 mW/cm² of waste heat, thefirst operating condition providing a current density of at least about150 mA/cm², and an effective amount of an endothermic reaction isperformed to maintain a temperature differential between the anode inletand an anode outlet of about 80° C. or less (e.g., about 60° C. orless); 1) the molten carbonate fuel cell is operated at a voltage V_(A)of about 0.60 Volts to about 0.67 Volts (e.g., about 0.60 Volts to about0.65 Volts, about 0.62 Volts to about 0.67 Volts, or about 0.62 Volts toabout 0.65 Volts), the molten carbonate fuel cell optionally beingoperated at a fuel utilization of about 65% or less; m) the cathodeinlet stream comprises at least a portion of a combustion turbineexhaust, at least a portion of the anode exhaust being recycled into theanode; n) the cathode inlet stream comprises at least a portion of acombustion turbine exhaust, at least a portion of the anode exhaustbeing used as an anode recycle fuel for a combustion zone of thecombustion turbine, an optional second fuel stream for the combustionzone of the combustion turbine optionally comprising at least about 30vol % CO₂ and/or at least about 35 vol % of a combination of CO₂ andinerts (e.g., at least about 40 vol % of a combination of CO₂ andinerts, at least about 45 vol % of a combination of CO₂ and inerts, orat least about 50 vol % of a combination of CO₂ and inerts); o) thecathode inlet stream comprises at least a portion of a combustionturbine exhaust, at least a first portion of the anode exhaust beingused as an anode recycle fuel for a combustion zone of the combustionturbine, and at least a second portion of the anode exhaust beingrecycled into the anode of the molten carbonate fuel cell; p) thecathode inlet stream comprises at least a portion of a combustionturbine exhaust, the cathode inlet stream comprising at least about 20vppm of NOx, and a cathode exhaust comprising less than about half ofthe NOx content of the cathode inlet stream; q) the method furthercomprises combusting at least a portion of the H₂-containing gas streamto produce electricity, the combusting optionally being done in acombustion zone of a second turbine, and the cathode inlet streamoptionally comprising at least a portion of a combustion turbine exhaustgenerated by combustion of a carbon-containing fuel; r) the methodfurther comprises reacting at least a portion of the syngas-containingstream in the presence of a methanol synthesis catalyst under effectiveconditions for forming methanol to produce at least onemethanol-containing stream and one or more streams comprising gaseous orliquid products, and optionally recycling at least a portion of the oneor more streams comprising gaseous or liquid products to form at least aportion of the cathode inlet stream; s) the method further comprisesoptionally sending one or more CO₂-containing streams derived from oneor more first refinery processes to the cathode inlet, separating CO₂from at least a portion of the anode exhaust to form a CO₂-rich gasstream having a CO₂ content greater than a CO₂ content of the anodeexhaust, and a CO₂-depleted gas stream having a CO₂ content less thanthe CO₂ content of the anode exhaust, and delivering the CO₂-depletedgas stream to one or more second refinery processes; t) the methodfurther comprises separating CO₂ from at least a portion of the anodeexhaust to produce a CO₂-rich stream having a CO₂ content greater than aCO₂ content of the anode exhaust and a CO₂-depleted gas stream having anH₂ content greater than an H₂ content of the anode exhaust, and using atleast a portion of the CO₂-depleted gas stream in an ammonia synthesisprocess, in a process for synthesis of an organic nitrogen-containingcompound, or in both; u) the method further comprises withdrawing, froman anode exhaust, a first gas stream comprising CO, the anode exhausthaving a pressure of about 500 kPag or less, introducing the first gasstream withdrawn from the anode exhaust into a process for production ofiron and/or steel, and optionally withdrawing a second gas streamcomprising H₂ from the anode exhaust and, if withdrawn, using the secondgas stream as fuel for heating in the process for production of ironand/or steel; v) the method further comprises generating an anodeexhaust comprising H₂, CO, H₂O, and at least about 20 vol % CO₂,reacting at least a portion of the anode exhaust under effectiveFischer-Tropsch conditions in the presence of a shifting Fischer-Tropschcatalyst to produce at least one gaseous product and at least onenon-gaseous product, wherein a CO₂ concentration in the at least aportion of the anode exhaust is at least 80% of a CO₂ concentration inthe anode exhaust, and recycling at least a portion of the at least onegaseous product to the cathode inlet; w) the method further comprisesgenerating an anode exhaust comprising H₂, CO, CO₂, and H₂O, and havinga ratio of H₂ to CO of at least about 2.5:1, reducing the ratio of H₂ toCO in at least a portion of the anode exhaust to a ratio of about 1.7:1to about 2.3:1 to form a classic syngas stream, which also has a CO₂concentration that is at least 60% of a CO₂ concentration in the anodeexhaust, reacting the classic syngas stream under effectiveFischer-Tropsch conditions in the presence of a non-shiftingFischer-Tropsch catalyst to produce at least one gaseous product and atleast one non-gaseous product, and optionally recycling at least aportion of the at least one gaseous product to the cathode inlet; and x)the method further comprises generating an anode exhaust: comprising H₂,CO, and CO₂, having a ratio of H₂ to CO of at least about 2.5:1, andhaving a CO₂ content of at least about 20 vol %, removing water and CO₂from at least a portion of the anode exhaust to produce an anodeeffluent gas stream, the anode effluent gas stream having aconcentration of water that is less than half of a concentration ofwater in the anode exhaust, having a concentration of CO₂ that is lessthan half of a concentration of CO₂ in the anode exhaust, or acombination thereof, the anode effluent gas stream also having a ratioof H₂ to CO of about 2.3:1 or less, and reacting at least a portion ofthe anode effluent gas stream over a non-shifting Fischer-Tropschcatalyst to produce at least one gaseous product and at least onenon-gaseous product.

Embodiment 2

The method of embodiment 1, wherein the cathode inlet stream comprisesat least a portion of the anode exhaust, at least a portion of any gasstream withdrawn from the anode exhaust, or a combination thereof.

Embodiment 3

The method of embodiment 1 or 2, wherein the cathode inlet streamcomprises at least a portion of an exhaust from a combustion reaction,an exhaust from a combustion turbine, or a combination thereof.

Embodiment 4

The method of any of the above embodiments, wherein CO₂ is separatedfrom the anode exhaust, from any gas stream withdrawn from the anodeexhaust, or a combination thereof, at least a portion of the separatedCO₂ optionally being combined with a at least a portion of thefermentation exhaust.

Embodiment 5

The method of any of the above embodiments, wherein H₂O is separatedfrom the anode exhaust, from any gas stream withdrawn from the anodeexhaust, or a combination thereof.

Embodiment 6

The method of any of the above embodiments, further comprisingseparating H₂O from the anode exhaust, and using the separated H₂Oduring the processing of the biomass to produce the at least onefermentation product.

Embodiment 7

The method of any of the above embodiments, wherein generatingelectricity within the molten carbonate fuel cell comprises operatingthe fuel cell at a fuel utilization, the fuel utilization being selectedbased on at least one of an electrical demand of the processing of thebiomass, a heat demand of the processing of the biomass, and a heatdemand of the distillation of the fermentation product.

Embodiment 8

The method of any of the above embodiments, wherein the reformable fuelis derived from biomass by anaerobic digestion of biomass residueproduced by the processing of the biomass.

Embodiment 9

The method of embodiment 8, wherein at least some of the reformable fuelis derived from biomass by partial oxidation and/or gasification ofbiomass residue produced by the processing of the biomass.

Embodiment 10

The method of any of the above embodiments, wherein the at least onefermentation product comprises ethanol.

Embodiment 11

The method of any of the above embodiments, further comprisingseparating from an anode exhaust a CO₂-rich stream, and using theCO₂-rich stream as part of a photosynthetic algae growth process.

Embodiment 12

The method of any of the above embodiments, wherein the reformable fuelis derived from algae biomass generated in an algae growth pond.

Embodiment 13

The method of any of the above embodiments, further comprisingseparating from an anode exhaust a CO₂-rich stream, and sending at leasta portion of the CO₂-rich stream to the cathode inlet.

Embodiment 14

The method of any of the above embodiments, wherein at least some of theheat for distillation is provided based on combustion of a fermentationproduct.

Embodiment 15

The method of any of the above embodiments, wherein the anode exhausthas a molar ratio of H₂:CO of at least about 3.0:1.

Although the present invention has been described in terms of specificembodiments, it is not so limited. Suitable alterations/modificationsfor operation under specific conditions should be apparent to thoseskilled in the art. It is therefore intended that the following claimsbe interpreted as covering all such alterations/modifications that fallwithin the true spirit/scope of the invention.

What is claimed is:
 1. A method for producing electricity, and hydrogenor syngas, using a molten carbonate fuel cell comprising an anode andcathode, the method comprising: introducing a fuel stream comprising areformable fuel into the anode of the molten carbonate fuel cell, aninternal reforming element associated with the anode, or a combinationthereof; introducing a cathode inlet stream comprising CO₂ and O₂ intothe cathode of the molten carbonate fuel cell; generating electricitywithin the molten carbonate fuel cell at a fuel utilization of about 65%or less and at a cell operating voltage, a ratio of a cell operatingvoltage to a cell maximum voltage being about 0.65 or less; andgenerating an anode exhaust from an anode outlet of the molten carbonatefuel cell; and separating from the anode exhaust a H₂-containing stream,a syngas-containing stream, or a combination thereof, wherein areformable hydrogen content of the reformable fuel introduced into theanode, the internal reforming element associated with the anode, or thecombination thereof, is at least about 75% greater than an amount ofhydrogen oxidized to generate electricity.
 2. The method of claim 1,further comprising reforming the reformable fuel, wherein at least about90% of the reformable fuel introduced into the anode of the moltencarbonate fuel cell, the internal reforming element associated with theanode of the molten carbonate fuel cell, or the combination thereof, isreformed in a single pass through the anode of the molten carbonate fuelcell.
 3. A method for producing electricity, and hydrogen or syngas,using a molten carbonate fuel cell comprising an anode and cathode, themethod comprising: introducing a fuel stream comprising a reformablefuel into the anode of the molten carbonate fuel cell, an internalreforming element associated with the anode, or a combination thereof;introducing a cathode inlet stream comprising CO₂ and O₂ into thecathode of the molten carbonate fuel cell; generating electricity withinthe molten carbonate fuel cell at a fuel utilization of about 65% orless and at a cell operating voltage, a ratio of a cell operatingvoltage to a cell maximum voltage being about 0.65 or less; andgenerating an anode exhaust from an anode outlet of the molten carbonatefuel cell; and separating from the anode exhaust a H₂-containing stream,a syngas-containing stream, or a combination thereof, wherein the moltencarbonate fuel cell is operated to generate electrical power at acurrent density of at least about 150 mA/cm² and at least about 40mW/cm² of waste heat, the method further comprising performing aneffective amount of an endothermic reaction to maintain a temperaturedifferential between an anode inlet and the anode outlet of about 100°C. or less.
 4. The method of claim 1, wherein a CO₂ utilization of thecathode is at least about 50%.
 5. The method of claim 1, wherein theanode fuel stream comprises at least about 10 vol % inert compounds, atleast about 10 vol % CO₂, or a combination thereof.
 6. The method ofclaim 1, wherein the anode exhaust comprises H₂ and CO having a molarratio of H₂ to CO from about 1.5:1 to about 10.0:1.
 7. The method ofclaim 6, wherein the anode exhaust has a molar ratio of H₂:CO from about3.0:1 to about 10:1.
 8. The method of claim 1, wherein the H₂-containingstream contains at least about 90% H₂.
 9. The method of claim 1, whereinthe cathode inlet stream comprises about 20 vol % CO₂ or less.
 10. Themethod of claim 1, further comprising recycling at least a portion ofthe H₂-containing stream to a combustion turbine.
 11. The method ofclaim 1, wherein at least about 90 vol % of the reformable fuel ismethane.
 12. The method of claim 1, wherein the molten carbonate fuelcell is operated at a thermal ratio from about 0.25 to about 1.0. 13.The method of claim 1, wherein a ratio of net moles of syngas in theanode exhaust to moles of CO₂ in a cathode exhaust is at least about2.0:1.
 14. The method of claim 1, wherein a fuel utilization in theanode is about 50% or less and a CO₂ utilization in the cathode is atleast about 60%.
 15. The method of claim 1, wherein the molten carbonatefuel cell is operated to generate electrical power at a current densityof at least about 150 mA/cm² and at least about 40 mW/cm² of waste heat,the method further comprising performing an effective amount of anendothermic reaction to maintain a temperature differential between ananode inlet and the anode outlet of about 100° C. or less.
 16. Themethod of claim 15, wherein performing the endothermic reaction consumesat least about 40% of the waste heat.
 17. The method of claim 1, whereinan electrical efficiency for the molten carbonate fuel cell is betweenabout 10% and about 40% and a total fuel cell efficiency for the moltencarbonate fuel cell is at least about 55%.
 18. The method of claim 3,wherein a reformable hydrogen content of the reformable fuel introducedinto the anode, the internal reforming element associated with theanode, or the combination thereof, is at least about 75% greater than anamount of hydrogen oxidized to generate electricity.
 19. The method ofclaim 3, wherein performing the endothermic reaction consumes at leastabout 40% of the waste heat.